Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 1 , J. Brook Chemistry 1 and Physics Discussions Atmospheric 1 erences. These pressure ff , K. L. Hayden 2 , and H. He 1 , D. Sills 1 ect on air pollution. For large bodies of ff 14242 14241 , C. Stroud , D. W. Tarasick 1 1 , W. Gong 1 , M. D. Moran 1 , J. Zhang 1 erin Street, Toronto, Ontario, Canada , C. Mihele ff 1 erin Street, Toronto, Ontario, Canada ff and Physics (ACP). Please refer to the corresponding final paper in ACP if available. This discussion paper is/has been under review for the journal Atmospheric Chemistry National Laboratory for Nowcasting and Remote Sensing Meteorology, Environment Canada, Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 the warm season.water Air is warmed over much the less, land resulting is in warmed local after pressure sunrise di while the air over the regional ozone levels. High-resolutionthese local-scale modelling features is in recommended operational air-quality in forecasts. order to predict 1 Introduction The local and mesoscaleland circulations that versus arise water from canwater contrasts have (oceans, in large a the lakes), significant heat a capacity e diurnally of varying circulation frequently develops during mass tracking of modelcombined transport with shows the synoptic that flow lake-breeze canters carry surface ozone from convergence and these zones its source precursors hundreds areas,mesonet of in kilome- ozone narrow, elongated observations features. confirmfeatures, Comparison which the with create surface presence, local magnitude, ozone and enhancements timing on the of order these of 20 ppbv above the the photochemical production and transportprovements of in ozone model at correlation the withhighest local ozone spatial scale. resolution. observations Significant Mass are im- tracking achieved ofErie in individual model going and processes to show St. that the Lakes Clairmid-day production frequently rates act of asover 6 these photochemical to two 8 production ppbv lakes regions, per infields hour. 23-day-average with and surface aircraft Enhanced average ozone measurements ozone fields.levels levels suggests over Analysis are Lake that St. of evident vertical Clair other while recirculation model strong enhances subsidence enhances ozone ozone over Lake Erie. The A three-level nested regional air pollutionleading model to has been high usedAmerica. to ozone study The concentrations the processes highest in resolutionthe the simulations lake show southern breeze that circulation Great complex and interactions Lakes the between region synoptic flow of lead North to significant enhancements in Abstract 2 4905 Du Mass tracking for chemical analysis:causes the of ozone formation inOntario southern during BAQS-Met 2007 P. A. Makar Received: 28 April 2010 – Accepted:Correspondence 26 to: May 2010 P. A. – Makar Published: ([email protected]) 9 JunePublished 2010 by Copernicus Publications on behalf of the European Geosciences Union. Atmos. Chem. Phys. Discuss., 10,www.atmos-chem-phys-discuss.net/10/14241/2010/ 14241–14312, 2010 doi:10.5194/acpd-10-14241-2010 © Author(s) 2010. CC Attribution 3.0 License. I. Levy 1 Du 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - ff and high 2 ´ an et al., 1997; ected by the sea- cient to induce the ff ects) to provide suf- ffi ff ected by sea-breezes was sup- ect on ozone forecasts than, for ff ff ¨ uck et al., 2008). Cluster analysis of surface 14244 14243 ected by sea-breeze-enhanced ozone levels. ff cient to induce this circulation (Laird et al., 2001). In cient photochemical reactor (Puygrenier et al., 2005). ffi ffi C are su ◦ ´ in the Marseille marine boundary layer (indicative of a more photochemically aged an et al., 2000). erences drive a local circulation, with air descending over the water and rising over The city of Marseille has been another focus for sea-breeze induced meteorologi- Houston is sometimes severely a Non-reactive tracer modelling studies of coastal Los Angeles noted the ability of 3 ff (Pirovano et al., 2007). hibited by topography, the latter enhancedO by topography. Relatively low NO airmass) suggest that it isPollutant an concentrations in e Marseille maximizefront just upwind propagation of speed the sea-breeze isthe front lower front (the than is the lessaccumulate wind than just behind speed, the the and horizontal front,The the flux with accurate some vertical within simulation upward the mass of transport;in the sea-breeze, (Drobinski flux the et fine-scale allowing at Marseille al., features pollutants area 2007). of is to sea-breeze crucial mesoscale in transport order to predict both ozone peaks and ozone plumes region suggests that Marseille’sbreeze: urban heat the island urbanpressed circulation circulation relative is to when a instances theal., of city 2006a; synoptic Drobinski was flows et a originatingsuggested al., the over 2007). presence the of Work land “deep” and by (Lemonsu “shallow” the et sea-breeze same circulations, the group former (Lemonsu in- et al., 2006b) example, the choice ofal., plume rise 2008). parameterization The insea-breeze placement an locations of air-quality also has major model a emissions (Cheng significantin impact et sources the on Greater relative both Houston ozone to formation area regularly and (Byun dilution repeating et al., 2007). cal and air pollutionsea- studies. and lake-breezes High interactepisodes resolution with (Lasry modelling Marseille’s et studies VOC al., have 2005). emissions suggested to Sophisticated that urban create heat high island ozone modelling for the same and sea-breezes in oppositionto to recirculation the of processed synoptic airbreeze flow fronts (Banta lead onto et land to al., is dependant the 2005).the on highest local the The direction radiative pollution, depth of balance of due the andand synoptic penetration wind, land of these as surface sea- well factors characteristics; as in on (Cheng turn and Byun, have 2008), a more significant e of the sea-breeze front is the key factor in predicting high pollution events in Houston, one hour, up to six hours before the ozone event (Darby, 2005). The timing of the arrival autumn (Cheng, 2002), Houston(Mestayer (Banta et et al., al., 2005; 2005),Mill Lasry Vancouver (Li, et 2004), al., Marseille 2005) , Madrid andAnalyses Valencia of (Mill surface winds,have showed upper that level the highest synoptic ozone mapssea-breeze days in fronts and that (Darby, city meteorological 2005; are Rappengl conditions associatedwinds with showed the that passage these of events correspondshore to to the onshore situation wherein flow transition is from separated o by a period of stagnation greater than or equal to layers of high concentration pollutants(Lu with the and onset Turco, of 1995). morestudies stable conditions in This at coastal finding night environmentswith has (cf. respect also Li, to been 2004). found theshown The to in synoptic give sea numerous rise flow, or to measurement but lake elevated pollution combinations breeze levels. of is Example locations the often include weak two Taiwan in have the frequently been onto land may sometimes createhumidity a and sharp gradient atmospheric in stability; temperature,contrasts a wind less lake speed, than relative (or 12 sea)light breeze winds, front. temperature constrasts Air-lakecirculation temperature of – only as a synoptic wind few speeds degrees increase, are larger su contrasts aresea-breeze-induced fronts required. (sometimes coupled with topographicficient e vertical transport to loft pollutants to high levels during the day, in turn creating the land during the day, withdivergence the reverse at occurring at the night. surface Thisreturn over in circulation turn the aloft. induces water, daytime Thewind surface daytime flow convergence surface is over divergence known the and asto land, associated the as lake- water-to-land with the or a land sea-breeze, breeze while (cf. the Stull, reverse 1988). circulation is The referred leading edge of the intrusion of marine air di 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | cient to determine the cause of high ozone ffi 14246 14245 , suggesting both local and long-range transport x cient magnitude to prevent significant recirculation of aged ffi and VOCs suggested that the airmass associated with the ozone maxima x A common factor of the work to date on lake- or sea-breeze fronts is their com- The reactive ozone chemistry associated with lake-breeze fronts in southern Ontario Observational studies of lake-breeze fronts and their impacts on air pollution in the The two main mechanisms for venting of Marseille’s boundary layer air to the free Recirculation of aged polluted air in sea-breeze fronts has been observed elsewhere, The surface temperature during the passage of Marseille’s sea-breeze front has which follows, we use nested meteorological and pollution models to analyze ozone tion and satellite observationsdetailed to analysis the (Hastie et passagecursor al., of NO 1999). a Time-coincident lake-breeze aircraft frontwas measurements well-aged, in of and a moved pre- inland later, from more a position originating overplex Lake nature; Ontario. theyfound are impact very on local-scale surface ozone featuresmesoscale concentrations meteorological which in and nevertheless polluted air-quality models regions. mayalyzing have Three-dimensional have provided that a a complexity useful in pro- means Los of an- Angeles, Houston, Taiwan and Marseille. In the study was first examined in the1988) 1980’s suggested and that 1990’s. local Somenoted impacts of a on this more ozone early levels significant work were impactincreases (e.g., generally of (Mukammal Yap 30 small, et et ppbv while al., over al., the some 1982, course 1985). of a Ozone few concentration minutes were linked through surface sta- ulations of the airGaussian pollution associated dispersion with models lake of breezeels non-reactive circulation (Lyons tracers, started et but the with al.,10 limitations simple 1983) km of as led the these to drivers mod- the forlake-breeze non-reactive use circulation tracer was of dispersion found studies full to (Lyons be mesoscalepected; et considerably al., models more simulated 1995). complex at non-reactive than The resolutions tracer previouslytransported ex- of plumes out 1 released of to at thefront. the shallow lake-breeze Plumes shoreline inflow followed were helical layer entirely and upon even reaching bifurcating the trajectories lake-breeze (Lyons et al., 1995). lation, and an anti-correlation with NO sources of ozone. region of the GreatLyons and Lakes Cole of 1973, North 1976; Lyons America and began Olsson, 1973; in Anlauf the et 1960’s al., 1975). (Mukammal, Model 1965; sim- ozone levels is unclear, with high ozone levels occurring for both high and low recircu- which intensified it. The mechanism for sea-breeze impacts on eastern Mediterranean al., 2007). The same studytransport showed the in presence frontal of circulation ozone alongobservational aloft with evidence available for recirculation was downward not patterns always along su events the (e.g. coast, three but possible the sourceshas for an a event significant on 4 impact2008). August on 2004). As pollutants Recirculation in also alongflow the the was Marseille found eastern studies, to Mediterraneanof the govern (Levy urban the interaction et impact between heat al., of synoptic islandsthe the and former and sea reducing mesoscale the breeze sea-breeze shape intensity, on and of air the pollution. the latter coastline creating The convergence modified location regions the sea-breeze, with 2006). This venting is of su air back into the PBL (Drobinski et al., 2007). however. Along thefronts New has been England observed coastline, to increase recirculation ozone of concentrations by aged 10 to air 30 ppbv in (Darby sea-breeze et ing convection. The upward motion resultsthis in in surface turn level amplifies convergence the overincreasing the sea-breeze land flow, stability which – again, in turn and advectsattempts slowing cooler to forward air model motion over this the until observed land, al., the oscillatory 2007). cycle flow repeats. have been Recent unsuccessful (Drobinski et troposphere are upslope windssea-breeze front, enhanced with associated by turbulence sea and upward breezes, motion (Bastin and and Drobinksi, frontogenesis at the been found to betransported oscillatory inland (Puygrenier due et to sea-breezes al., resultsland 2005; in (isentrope temporarily Drobinski inclination increased et allows stability al., the overbatic the sea-breeze 2007). cooling flow associated Cold to with run air rising alongsolar the air energy slope, retards is and the transferred adia- flow). to the The surface, stability triggering is turbulent short-lived, vertical as transport includ- 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - ff cients ffi erent processes or approximately ff usion coe ff ◦ 641 grid points over × or approximately 2.5-km grid spac- ◦ 14248 14247 494 grid points, 0.0225 was installed in the study region, in addition to ozone and × 5 . 2 565 grid points over North America, 0.1375 × ´ e et al., 1998); (b) an emissions processing system, SMOKE (Sparse ˆ ot observations available from larger scale monitoring networks (AIRNow). 5 . 2 The multi-pollutant, regional AURAMS CTM was developed as a tool to study the for- The GEM meteorological model is an integrated weather forecasting and data assim- The work that follows has two main components. First, following a discussion on our The Border Air-Quality Study and Meteorology Study (BAQS-Met) was conducted in mation of ozone, PM, and acid deposition in a single “unified” framework. The PM size for the high-resolution domain meteorologicalolution simulations domain (Fig. was 1), and driven58 the by hybrid-coordinate coarse the levels res- operational from objective thecreasing analysis. Earth’s monotonically with surface height. The to The model 10 hPa, standardinclude employs version with a of layer GEM parameterization thickness 3.2.2 for was in- urban modifiedments to heating included a (Makar temperature-gradient-based et boundary al.,and layer 2006). height consistency parameterization, Additional improvements improve- forin the the model-generated lowest model vertical layers. di 3.2.2 with physics versionhorizontal 4.5 grid was with a runthe core on domain globe, two covering domains: with North15.3-km 432 America a grid (575 variable-resolution spacing in global thethe Great core Lakes region, area 450-s (565 timestep),ing, and 60-s a timestep). local domain The covering coarse-grid output was used to provide boundary conditions tiscale model: C Matrix Operator Kernel Emissions:line Houyoux regional et chemical transport al., model, 2000;cf. the CEP, AURAMS Cho 2003) Chemical et ; Transport Model al., and (CTM: 2009;et (c) al., Gong an 2008). et o al., 2006; Makar et al.;ilation 2009; system Smyth et that al., wasand 2009; designed medium-range Stroud to weather meet forecasts. Canada’s operational For needs the for both BAQS-Met short- simulations, GEM version 2.1 Modelling system description AURAMS (A Unifiedcomponents: Regional (a) Air-quality a prognostic Modelling meteorological System) model, GEM consists (Global of Environmental Mul- three main 2 Methodology and chemical causes for ozone formationconcentration in fields, the process region, using mass timeozone tracking, sequences time of and series model comparison (Sect. ofare 4). presented model The in and Sect. implications observed 5. of the analysis and concluding remarks average ozone and PM PM methodology (Sect. 2), we present aavailable data formal (Sect. statistical evaluation 3). of Second, the we model make using use the of the model output to infer the physical the region between Lakes Huron, St.of Clair, and lake Erie, breezes with the on aimcomprised local of studying a air-quality the and measurement-intensive impact long-range-transportedas field well chemistry. campaign as The from a study August. local 20 A monitoring June variety of network to measurements that forthree 10 particulate operated supersites matter (Bear from July Creek, and the gases Harrow 2007, and were monthsCouncil Ridgetown), carried of of on out Canada board June at the (NRC) through National Twin Otter Research mobile aircraft, laboratory and as on part Environment of Canada’s the CRUISER study. A ten-site mesonet monitoring network for 5-min the concept of mass-centration or (in operator-tracking, this in which case,model, the allowing ozone) us changes are to to quantitatively trackedtowards a state through ozone the pollutant’s formation every relative con- in importance operator the of of study di region. the air-quality formation in lake-breeze fronts in southern Ontario. As part of that analysis, we use 5 5 25 15 20 10 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ); 3 -NO p ); nitrate ( 4 -SO p road-mobile sources, minor point ff usion, gas-phase, aqueous-phase, and ff 14250 14249 ); elemental carbon (EC); primary organic matter (POM); secondary 4 -NH p The GEM meteorology was created in a sequence of 12 h runs, starting at 0, 6, 12 Files of gridded hourly emission fields for input by the AURAMS CTM were prepared A three level internal nesting setup was used for the AURAMS v1.4.0 simulations: domain time-step at eachmesonet ozone of site the 5-min fixed averages were station summed sites to of create hourly the averages, BAQS-Met and intensive. the The simulation made use of the 15-km GEM simulation as2.3 boundary conditions. Model diagnostics: extraction of model2.3.1 values and mass Extraction tracking of model values Times series of surface15-km ozone at AURAMS hourly simulations intervalsof for were surface comparison extracted ozone from to concentrations the AIRNow were 42-km observations. extracted and on the Time two series minute AURAMS 2.5-km and 18 Z from objectivesix analysis hours files of at these thoseretained times simulations for for being AURAMS the simulations. used 15-km This fordata simulation, methodology model assimilation makes the spin-up, use of first the of the the lastdrift objective meteorological six of analysis hours to the being the predicted maximum 15-km extent, to meteorology prevent from chaotic the observations. The 2.5-km GEM higher resolution GEM 2.5-kmAURAMS simulation, simulation. in The turnrun GEM used 2.5-km for to and dates drive AURAMSJuly encompassing the 2.5-km 2007). higher the simulations The resolution BAQS-Met were lateralsimulations measurement boundary only were conditions intensive taken for from (17 the thecase; 15-km June corresponding and the to coarser 2.5-km resolution climatological 11 AURAMS simulations CTM AURAMS boundary in simulations. condition each was used for the model top in all three Both GEM and the AURAMSto CTM 31 were run August forThe 2007, the GEM for 3-month 15-km period the from meteorology15 GEM km. 1 was 15-km June used The 2007 and to GEM AURAMS drive 15-km 42-km the meteorology AURAMS and was CTM also 15-km at used domains. both for boundary 42 conditions and for the 2.2 Simulation period and operating sequence being used to create these emissions during the model runs. although gaseous species, primarily ozone, will be the focus inusing the version current 2.2 work. ofsions streams: the on-road SMOKE mobile emissionssources; sources; processing and area and major system o point forspeciated sources. four within Emitted major the (i.e., emis- AURAMSstream. “primary”) CTM PM based The from on base thesefor speciation sources year Canada, profiles is for and for the 1999 eachalgorithms, anthropogenic for emissions with Mexico. emissions model Biogenic was generated temperatures emissions 2005 and are for photosynthetically calculated active the using radiation USA BEIS3.09 and chemical species, andvertically-varying the chemical outermost lateral domain boundaryeight also conditions terrain-following makes (Makar vertical use et levelsto of stretched al., 29 km, telescopically 2009). time-invariant with from and the Twenty- the(gases first and Earth’s three chemically levels surface speciated at 0, particle 13.9, size and bins) 55 may m be a.g.l. selected Up as to model 157 output, model species horizontal and vertical advection,inorganic heterogeneous vertical chemistry, secondary di organicdeposition, particle and formation, particle dry nucleation, and condensation,tivation wet coagulation, (Gong sedimentation, et and al., ac- 2006). 42-km/15-min North American domain,American in domain, turn in drivingAll turn a 15-km/15-min model driving Eastern resolutions a North make 2.5-km/2-min use Southern of Ontario a domain time-invariant (Fig. upper 2). boundary condition for the in Stokes diameter and nineammonium chemical ( components: sulphate ( organic matter (SOM); crustalis material assumed (CM); to sea be internally salt;1.4.0 mixed of and in the particle-bound each AURAMS CTM water. size include bin. PM emissions Process from representations surface in and from version elevated sources, distribution in this study was represented using 12 size bins ranging from 0.01 to 41 µm 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - ffi erential equa- ff ciently high to traverse (cf. Gipson, 1999; Jang ffi ciently slow that the nearest model ffi process analysis ciently accurate for comparison purposes. 14252 14251 ffi usion and deposition operators for ozone, within the AURAMS ff ries and Tonnesen, 1994). ff erent components (operators) of the net equation are solved in sequence, with the The ozone mean biases (MB, Table 1) are positive for all domains and sub-domains, ff simulations being more likely toresolution. capture part of a “near-miss” transport event than high is chosen to bedomain somewhat focused comparable to to the the intensive high-resolution field 2.5-km study resolution area. model but decrease with increasing resolution.imum, The daily mean mean, biases for and themean hourly model square values daily are error 1 h all also max- cient very decreases decreases similar with slightly for increasing with theplacement resolution. increasing same of resolution. grids. The events The correlation The becoming root coe latter more may frequent reflect at spatial higher mis- resolution; the low resolution ozone values, daily 1-haged average ozone statistics maxima, over and allare daily the mean presented. sites ozone within values. For theof Aver- two the green model line, 42-km domains Fig. resolutioncomparison and 2b) purposes, run, is two and, the chosen sub-domains for to the “eastern” be 15-km sub-domain resolution compatible (region run, to the left the “BAQS-Met” 15-km sub-domain resolution domain for 3 Model performance evaluation 3.1 AURAMS 42-km and 15-km ozoneHourly versus ozone AIRNow measurements observations from thepared near-real-time to AIRNow the metanetwork were 42-km com- andAugust 15-km 2007, AURAMS with output for the thefor results each period depicted AIRNow 3 site in June (nearest 2007 Table neighbour 1. through grid-cell 31 from Evaluation the statistics model) with are regard computed to hourly garding the reasons for theozone model’s formation, ozone predictions, destruction, hence and providing transport,has hypotheses in appeared for the elsewhere ambient in atmosphere. theet literature, This al, as concept 1995; Je simulations. The relative magnitude and sign of the operators thus give information re- tracking options allow comparison ofadvection, the and gas-phase the chemical production di and loss, the solution from each operator innext the sequence operator becoming in the initial thethe concentrations sequence. model. for the AURAMS Each v1.4.0mass component includes operates of an over selected analysis the package modelin that net mass species records for time through the each step each component changemay of of in of be the tracked the in model AURAMS; model atmosphere thesubsequent across mass operators. prior to each to of the The the these operator, operator change operators inerator is subtracted order for from to that the determine mass time the step net (which change is in then mass expressed for in that units op- of ppbv/hour). These mass 2.3.2 Mass tracking of ozone As is the casesplitting for (Marchuk, most 1975) for regionaltions the transport describing numerical models, the solution rate AURAMS of of makesdi change the of use system the of of chemical di constituents operator in the atmosphere: the each two minute model3-D step flight path were in used theinterpolated to model from extract coordinate the the system. model modelused The grid, to average values during create of along that the the corresponding 2 the ten min “model”data. same second value interval, The for values ozone along statistical measurements that comparison from to flight theaverages: the mobile path, the laboratory aircraft speed was CRUISER of were the onegridpoint mobile minute to laboratory the is su CRUISER location is su lent hourly averages for statistical analysis.2010) Aircraft were ozone five observations (Hayden secondparison et resolution to al., AURAMS’ data: output. these Theseveral model speed were of gridpoints binned the in to aircraftmodel a two was to two su minutes minute measurement for interval. locations, com- the In aircraft order locations to at more 10 closely match second the intervals during corresponding AURAMS 2.5-km/2-min output values were summed to create equiva- 5 5 20 25 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent averaging times), ff cient of 0.74, slope of 0.98, ffi , indicating that these ozone features have 1 − 8.4 ppbv, and a mean error of 12.3 ppbv. The 14254 14253 − cients relative to the lower resolution simulations of Table 1; ffi cients and slopes are improved relative to the monitoring network data ffi 7.4 ppbv, a mean bias of − cients (one sig. fig.) of less than 0.5. The flights with the lowest correlation co- 0.0, had the three largest positive intercepts of 62, 77, and 50 ppbv). Figure 4 ffi cients tended to have large positive intercepts (e.g. Flights 6, 7, 14, each having < To explore this issue further, the portion of Flight 2 (Fig. 4b) between 18:06 and Both the observations and the model show the presence of relatively short duration ffi magnitudes of the two peaks in the observations during the flight (5a), with the location observed ozone maximum isThe 52 ppbv, aircraft while trajectory the during model theline maximum given arrow is time (Fig. 35 interval ppbv 5b, is (Fig.titration c). shown in 5a). on The a the power-plant model figure plumewest as predictions (Lambton a of show power-plant, dotted low the Fig. ozone flightthe 5, concentrations track), plume point due over marked slight to the “A” ozone northLake to enhancement end the St. of in Clair Lake the St. andnearest downwind Clair model Lake (“B”), region level (Fig. Erie and south 5b) a (“C”). belowand of weak the The 37 ozone aircraft ppbv, observations and model-predicted ridge point 52 between ozone ppbv B and and concentration C 42 at ppbv are at 46 the ppbv, the next level up (Fig. 5c). Comparing to the 18:26 is examined inobserved more ozone detail time in series, Fig.18:20 5, as and which well 1235 shows as and 1500 a thelevels closest m close-up model-predicted to, a.g.l. and of ozone (approximately just the 1435 above, concentrations m the model at aircraft and altitude and 1700 during m this a.s.l.; portion the of model the flight). The cal flying speed of thetrough-to-trough Twin Otter spatial scales is of 60 28 m to s time 94 km. interval Superimposed events; on these for areof example, even shorter duration Flight 6 4 min (Fig. (21variation km) 4d) in with shows the peak-to-trough two same variationand simulated part of peaks the 20 of ppbv, each model the while thus the timethat suggest observed series accurate the is model presence about simulationsthese of 12 requires ppbv. durations small positioning and Both spatial-scale spatial errors the ozone scales. of observations features, no and greater than half of changes in the ozonefield. concentration, indicating For local-scale example, perturbations Flightations in 2 of the (Fig. ozone 15 4b) ppbvvariations shows over of peak-to-trough durations 30 ozone ppbv concentration of overshow 26 vari- 4 min a min, duration similar in Flight magnitude the 14 range observations, but (Fig. while over the 4n) a model shorter shows values duration peak-to-trough of about 8 min. The typi- biases for all flights.the Most figures) flights is have biased negative low mean relative biases; to the the observations model (white (thick diamonds). line on mean errors are similarthus to has the the monitoring tendency networkual to values. flight be statistics biased The were lower highduration generally for resolution and worse ozone model the aloft than than the impactcoe at overall of evaluation the very due surface. local toe Individ- sources; their 10 short out ofR 16 flights havingshows correlation the observed time series, simulated time series, correlation scores and mean sequence of flights, and forTable 3. individual flights, The to “All the Flights”intercept aircraft statistics of observations, show are a correlation shown coe in correlation coe in the aforementioned tables, though the biases have become more negative and the and the daily average,also daily constructed. 1hr average In maximum, Tablethe daily 2, model 1hr correlation the coe average increase minimum inmean were biases, model while resolution now negative, considerably aresimulations. improved also of lower magnitude than the lower resolution 3.3 AURAMS 2.5-km ozone versus aircraftStatistical observations comparisons between the 2.5-km/2-min AURAMS simulations and the entire Statistical comparisons betweenmesonet stations the shown 2.5-km/2-minsummary in statistics Fig. AURAMS across 3 simulations allobserved are stations and and given (some modelled in of the station which Table values 2. had were di first In summed order to to create create hourly a averages, set of 3.2 AURAMS 2.5-km ozone versus mesonet and supersite ozone observations 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | emissions for x source. Figure 8 com- x plume (from point A in Fig. 5) x culties inherent in the creation of high spatial 14256 14255 ffi titration region associated with the plume may therefore be misplaced in the model x The above examples illustrate the di Another possible cause for the low model ozone relative to observations during this Both model and observations showperiod a (20 tropopause June); fold ozone occurring concentrations at greater the than start 120 of ppbv the reach time elevations as low the observations at specific pointsused along to infer the the flight main path, processes the resulting model in predictions the3.4 may observed be ozone features. AURAMS 2.5-km ozone versus ozonesondeOzonesonde observations observations were carriedvals out during at the the study.of Ridgetown the Model supersite model profiles at simulations were 12model at h extracted the results inter- same from and times each the as horizontal observations the resolution ozonesonde are releases. compared The in 2.5-km Fig. 9 for the intensive period. riods is often mucherrors better in than the the placement performance andon for timing simulated specific of short concentrations local term circulation alongshows events events. that any may Small have careful given a analysis flightobservations large of to impact path. be the achieved: model Despite even output this, when allows the the a model example useful results interpretation do not of correspond the well to power-plant, but the modelfor magnitude the is winds biased modelthis high, winds power-plant to were possibly taken be duethat errors from more to in continuous northerly the the vertical emissions tendency thanNO placement monitoring and/or observed. dispersion data, of the suggesting NO simulation plume than have occurred. in the The real atmosphere, lowering the predicted ozoneand concentration. time resolved simulations of ozone: the model performance over longer time pe- and ozone production occurs too far south in the model. portion of the flightpares might observed be and excessive titrationobserved modelled from peaks NO the in during NO timing the – entire these flight: likely represent the the model NO peaks plume match from the Lambton reaching further south than observed hence (c) the transition between ozone titration model being too far east, hence (b) the model NO model wind fields at twoseries) levels over suggest the that lake the shownand presence in are of Fig. 7 generally significant (centre within changes portionwind in 30 of wind shears degrees the direction of with time with the heightdirection height, observations. changes on between The the 1210 model and north 1435on suggests m and the a.s.l. strong location south Both of model sides and theThe of observations region model’s agree of the failure wind to lake; predict directionthis 30 the change flight observed at to segment ozone the 45 peak’s southern (52 degrees ppbv, timingthus end 18:16 and of UT in magnitude the in part during flight. reality, be 35 ppbv, due 18:12 UT to in (a) the the model) predicted may location of the anticyclonic circulation in the air, with rapid changestime in wind series direction. for Figure thethe 7 18:00 observations UT shows along model the output. the observednortherly wind than flight At the direction the track observations, suggesting start shown thatplaced of in the about the modelled 10 Fig. anticyclonic time to circulation 6, series, 20 is km the compared too model to far winds to are the more east relative to the observed atmosphere. The also occurs. The modelat peaks the lead flight the speed observations of bythe the 2 aircraft min twin altitude (or otter). about are Thethe 8 model shown km vicinity wind in distance of fields Fig. this at 6: portionin the two of the the levels the wind bracketing complex flight direction naturelocal track occur of is anticyclonic the just shown. circulation local east At onthe wind of the flight the lower field the track elevation, in north-east start is reversals model. shore in of On a the of the region flight Lake south of side track, St. low of associated Lake Clair. velocity St. with horizontal Clair, wind a The the flight shear start track at crosses of both a levels region in of diverging the the model results mayproduction be region a at slight displacement pointbe in B due the relative to predicted in observations: location partone of the to the level model a ozone too under-prediction 10-km may high) horizontalnoted, however, (model error that too in the far statistical the west) comparison placement and shows of 1 that layer a the vertical systematic maximum (model negative at bias point B. It should be of the local ozone maximum “B”, one possible explanation for the underprediction in 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | has x ) 0.56). Ni- R cient ( cult to distinguish due ffi ffi 3.77 ppbv). The implication is − , respectively, for the entire period. 2 titration of ozone in the model. These x and NO 14258 14257 3 hourly average mean bias of 3 associated with the roadways’ mobile sources, but once the NO x cient frequency to be useful as archetypes for the given circumstances for ffi north of detroit lakes The ozone predictions for this study at mid and upper tropospheric levels, and the 22 ppbv, mean error 26 ppbv, RMSE 32 ppbv, correlation coe good correspondence in the locations of the main convergence lines in the vicinity The synoptic winds in thislake-breeze case front are lines from (the the south-west. lattercloud inferred Mesoanalysis analysis from wind the fields and and measured radarshown winds in fine-line as Fig. well analysis, 11. as see South satellite by of 23:00 Sills UTC Lake et (07:00 Erie, p.m. the al., localand lake-breeze daylight 2010, the front time). extends front under The up from lake-breeze review) towest Lake front 50 are of km St. west inland Lake of Clair Lake St. createthe Erie Clair. a synoptic region flow. The of Figure Lake weak 12inferred Huron shows surface from front the convergence is convergence corresponding to pushed wind regions the fields northwards in and over the fronts that (the wind lake latter fields) by predicted by GEM. There is a tional case studies are examined in Levy et al.,4.1.1 2010). 26 June 2007: Lake St. Clair lake-breeze front enhancement of ozone 4.1 Case studies We turn now totroposphere the use ozone of formation the inthe model the measurement as study intensive, an region. specific analysistended patterns tool to During to of recur, explain the circulation surface depending and three-weekwith and on ozone duration su lower concentrations the of synopticozone winds. formation. Three We examine specific these patterns archetypes occurred below with three case studies (addi- improves. 4 Model-predicted causes of ozone formation and destruction over the great been dispersed to the more rural locations of the mesonet, the fit to the observations that the model inemitted its NO current form is unable to capture the very local mixing of freshly and c compare modelAURAMS and ozone observed along O theing CRUISER all driving two routes minute model is− values generally with biased corresponding averaged low observations: (compar- trogen mean dioxide bias was biasedozone high values (Fig. are 10c), the suggestingbiases result that are of the much excessive negative more NO biasescompare negative in to than the Table that 1, seen O at the surface mesonet stations (e.g. 3.5 AURAMS 2.5-km ozone versus CRUISEROzone observations and other observations were madealong on roadways the in CRUISER the mobile laboratory, region, in ortown transit parked Windsor. along roadsides, CRUISER observation driving sites, routes or in during down- the intensive are shown in Fig. 10a, b during the measurement intensive is presented in He etdependence al. (2010). of these predictionsconditions on are the prescribed manner have been in theelsewhere which focus in of upper a and this separate lateral researchbetween issue project, boundary surface (Makar reported ozone et networkvertical al., location data 2010, of and the under profiles observationsmeteorological review). of model’s was ozone predicted found climatologies tropopause Briefly, (Logan, height. by the 1999) modifying in best accord the match with the dication of which may be presentto in missing the data. observations, In but thekm are model di level, while results, the these observations highMost show concentrations a of extend shallower down the penetration, to to measurement thetions about period 4- the and shows 8-km model level. a predictions. reasonable A comparison detailed between study observa- of stratospheric/tropospheric exchange as 8 km a.g.l. in the observations. The model shows two later similar events, some in- 5 5 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | -shore for ff ). Figures 13a, b show f 100 ppbv) ozone starts to appear by > 14260 14259 of Grand Bend, but these remain o vicinity along the cross-section (14c and 14e show no ozone produc- ff usion) along this second cross-section ( ff di + along lake-breeze frontal convergence zones This analysis has several common features with the other examples of model- Figures 13 and 14 predict that the region of greatest ozone formation on that day Mass tracking of gas-phase production and loss versus total transport can be used 46 ppbv during the ozone maximum at Grand Bend (15c). This large negative bias is 27 June, 8 July and2010, 9 under July review); were moderate days south-westerly with synoptic “high winds deformation” coupled lake with breezes strong (Sills lake et al., afternoon (b) lake-breeze frontsprecursors at that the result surfacevergence in and zone, local subsequent similar convergence lofting to ofconcentration of Drobinski continuing et these both in al. species ozone the (2007) in convergence and having (c) zones, the shut early despite down frontal photochemical evening earlier. con- production increases in ozone 4.1.2 8 July, 2007, 9 July 2007, 27 June, 2007: long-range transport of ozone Lambton power plant plume. predicted lake-breeze front ozoneozone formation photochemical which production follow just in outsideanalysis precursor subsequent we source sections: show regions that (a) (in on subsequent average these regions maximize over the lakes) in the early 15 ppbv at Paquette Corners− (15a) and Bearapparently Creek due (15b), to while apredicted the small concentrations error model in in is the the area biased the at wind three 18:00 direction. UT site and Figure locations. 23:00 15d, UT, Highpredicted respectively, along e ozone by with concentrations shows the downwind the of model model- most the in of Sarnia the the plume day, are andobservations. come The on-shore model to results the suggest north-east that of the the high station, values in are contrast associated to with the the surface convergence region. will be on the USto side model of predictions the in border. Fig.(Sombra Observed station, 15, surface Fig. ozone for 3, on sites was 26 not arranged operating June from that is south day). compared to Model and north observations near are within the border Note the wind-fields of Fig. 13b, which show the vertical transport associated with the of Lake St. Clair (13e) has combined with the Detroit plume (14b) further downwind. ward wind vectors at thesecity points). by Ozone photochemical is photochemically productionof created (13c northeast these and of photochemical e, the production positivetial regions values), correspondence (13d and between and is positive f, transportedshows values negative in the out values; 13c same note and fields theproduction 13e, spa- as has respectively). Fig. shut 13, Figure o but 14 tion at and 23:00 small UT regions (07:00 of p.m.the surface local convergence titration), time): but region ozone to gas-phase transportof its continues flow. boundaries to move By (14d from 07:00 and p.m. f) a and dome forward of along high the concentration direction ozone formed earlier to the west (d) total transport of ozonedestruction along along a the second cross-section, cross-section (e)ozone closer photochemical (advection to production Detroit and (C–D), andthat total high transport of concentration ozonealong occurs line in A–B, regions Fig. of 13a) surface and convergence consequent (points lofting a, (points b a and b, Fig. 13b, note up- to show that the ozonevergence is downwind created of photochemically in the the productionozone early region concentration afternoon, is that but responsible occur later for con- thereafter furtherof (similar ozone increases to and in the precursors the behind-front notedpredicted by net 18:00 UT Drobinski convergence (02:00 et p.m. local al., time)(b) 2007). (a) ozone surface Figure concentration gas-phase 13 ozone and shows concentrations, wind14a), the fields model- (c) along photochemical a production cross-section and north destruction of of Detroit ozone (A–B along in the cross-section, though GEM tended to overpredict convectionFigures during this 13a period (gust and fronts 14afields in Fig. at show 12). the the same corresponding02:00 p.m. times. model-predicted local ozone High time concentration concentrationtime (Fig. (14a). ( 13a), and continues to increase through 07:00 p.m. local of the lakes between measurements and observations (compare Figs. 11 and 12), 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | value R cult to accurately ffi 14262 14261 While these regions of enhanced ozone are relatively small (10’s of km across, As in Sect. 4.1.1, the above analysis suggests that the surface convergence zones The model’s corresponding predictions for gas-phase photochemical production and example of this can be seen in the measurement record for 9 July. Figure 20 shows the (hundreds of km) downwindtually of fumigate the downwards, source dependingthe regions. on ozone aloft conditions These might further ozone belayer downwind plumes brought growth, (for to may or the example, even- the surfacecirculation). on ozone a aloft subsequent may day during be boundary caught up inthough a up downwind to urban 250position km heat relative long, island to in the thetoring ambient above network atmosphere, example), sometimes observations and capture from may very the be similar mesoscale di features moni- in the ozone time series. An wind of precursor sourcecentrations in regions the by convergence region, confiningOzone similar concentrations and to are the also hence findings enhanced increasing even ofand further Drobinski precursor its downwind et via con- precursors al. transport (2007). along oftion ozone the ozone convergence may line. become detached Extended from features the of surface, and high travel concentra- considerable distances removing ozone from theseof photochemical blue areas, production Fig. regions 19b, d, (notetrations to at correspondence red elevations areas, above 19a, 1600 c).production m Transport and areas increases downwind (red the and ozone areas, concen- adjacentport 19b, to terms d). suggests the that Three photochemical they dimensional arethe driven surface highest by plotting the transport local of levels flow the are rather than along trans- the the synoptic convergence winds; line. associated with lake breezes will increase photochemical ozone production just down- is photochemically created (Fig.above 19a, the surface, c) near between theThe the cities ozone production surface and regions downwind and are ofbetween heights sometimes the detached 1000 of region from and 1600 the north m 1400 surface,curring of m. with Lake near maxima St. Figure the Clair. surface 19c over also Lake shows Huron. significant ozone Transport (both production horizontal oc- and vertical) is loss, and total transport, are shown in Fig. 19. The panels of Fig. 19 show that ozone and (“D”) the high ozone concentrationsof reaching Toronto. the locally-produced The ozone cross-section of(“E” the between to city Lake “F”) Huron suggests that and highin Lake concentration the Erie ozone vicinity is across of associated this with thealigned feature helical lake-breeze along circulation fronts the (Fig. length 18a,of of b that the shows flow, shows convergence that a zone, thebecoming clockwise wind while detached circulation field 18c, at from is looking 1000 the largely mhelical in aloft surface the transport at in direction “B”, pattern response with(Lyons has to plumes et of these been al., ozone 1995). circulation noted patterns. in other This high resolution model simulations concentrations at the surface (18a)more show an northern elongated of feature of theToronto high two cross-section ozone convergence (18b) along lines the shows: throughthrough (“A”) southern elevations high up Ontario. ozone to concentrations Theozone 1500m from Detroit further north the – downwind, of surface (“C”) Lake St. a Clair, region (“B”) where a high second ozone region concentrations of occur high aloft, the mesoanalysis, but the latterto was limited the due south to of theozone lack Lake of Huron. comparison meteorological indicators at Figurebiased 17 two low shows stations for the both (Sombra, model stationsstation, versus 17a, where at observations both night. and model surface and The Croton, measurementsof model show 17b). small fit ozone time during on duration the enhancements The theozone day model fields is order better at is of at theto 20 Sombra ppbv surface Toronto (18b) (18a) at and and midday. the two second Figure cross-sections, from the 18 Lake first shows Huron from to the North Lake model-predicted St. Detroit Clair (18c). The ozone here as an exampleof (note the that flight simulations). Flightshows 15 Figure the on 16a model-predicted shows 8 wind the July,(01:00 fields p.m. mesoanalysis Table local 3, and front time). locations surface has A and convergence theto similar regions 16b pattern highest the at is north predicted 17:00 UT (16b) of – Lake the model St. shows Clair the front extending much further to the north-east compared to breezes reaching far inland and downwind of the lakes themselves. 8 July is examined 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 100 ppbv) build titration from the > x cient Lake Erie ozone being ciently far inland compared to ffi ffi 14264 14263 erent sources, Croton (22b) largely from production down- ff predicted wind fields onthe the model same Lake day Erie (23b).observations lake-breeze The front (compare observed penetrates front winds insu symbols (23a)shows in the 23a suggest gas-phase to that ozone convergence and linesstronger destruction in advection predicted 23b). by from the Figure Lakether model 23c Erie at west the may in same move the time; ozone the ambient production Detroit region atmosphere to titration/production than come line on-shore.22:00 in UT The the fur- in model simulation, low Fig. bias and 22fadvected between allow onto may 17:00 UT land the therefore and in be Lake the the Erie model result simulation. of insu (22d) maxima arethe biased ozone high concentrations relative exitingobserved to Lake ozone St. the maxima Clair. observations; areriod At very the 13:00 EDT similar, Leamington model to though (22f), 18:00 the overpredicts the EDTshown model (17:00 in model to is Fig. and 22:00 23, biased UT). which low The compares likely for reason the the for mesoanalysis pe- this for low that bias area is (23a) to the model- on 6 July. The concentrationexperiences contours ozone and from wind di fieldswind suggest that of each the of Lambton theseHuron sites and lake-breeze front Sarnia (note emissions convergenceFig. sources of 22a wind being fields and carried north-west 22c). southozone of build-up station by Lighthouse over CRO the Cove Lake in (22d), Lake St.and meanwhile, Clair from (22c). experiences Detroit. the Leamington experiences outflow Crotonof flow from time from greater Lake series duration Erie (22b) in show the a observations “plateau” than of the ozone concentrations model simulation. Lighthouse Cove The last of thewith three photochemical circulation processing patternsshows over, observed and in the the transport model modelhouse from, ozone output Cove Lake and is (22d) St. associated wind and Clair. Leamington fields (22f) (Fig. Figure observed 22a, 22 and c, modelled e) ozone time and series Croton (22b), Light- 4.1.3 5 July, 6 July 2007: Lake St. Clair ozone production dome Sect. 4.2. concentration pattern in Fig. 21better is fit mostly of the the result of modelthat the time the local series earlier circulation at pattern. 17:00divergence” Croton UT The event (Fig. “north at 20a) of Sombra than Lake (Fig.Croton at 21a, St. Sombra station b, (20b) Clair” does d) suggests event not areThe and biased experience observation the high the time later, in first series “Lake thelation event, St. shows model are but that Clair simulation. capable does of very enhancingthe experience local the surrounding the events ozone regions. associated second. concentrations The with by modellinked about lake to simulations 20 circu- the suggest ppbv local that relative circulation these to in events are the vicinity closely of the Lakes. Further comparisons follow in 20 ppbv ozone “spike” inquent drop the in observation ozone record concentrationsLambton at at plume both at 20:00 UT Sombra, stations and results (21c, aof from larger 20a). the NO scale ozone decrease The formation at Croton and subse- ozone (21d). loss is Mass processes photochemically tracking (not created shown) on for the these times west shows side that of the Lake St. Clair – the high ozone shows the model-predicted surface ozoneLake concentrations St. and wind Clair fields on downwindand 9 of 06:00 p.m. July local at time,face 17:00, respectively), stations as 19:00, corresponding well to 20:00, as the and(Fig. time the series 21a, locations 22:00 UT of b), of Fig. and Sombra the 20. stationon two 20:00 From UT (SOM) ozone the 17:00 experiences (1, sur- through north high 19:00 3, side UT ozoneup of 4 associated in Lake with the St. a region Clair. region ofozone Very surface region divergence high intensifies over ozone and the concentrations lake is ( itself, advected at NE 17:00 over UT Lake (21a). St. This Clair high (21b), resulting in the The Croton time seriesozone (20a) event shows (circled that in thegetting red) model very close captures well, to a lagging the Lakethe the St. Sombra same observations observation Clair-derived magnitude by time and series aboutmodel shows an shape ozone that has hour, of only enhanced but one the ozone event both observed was before sampled, and event. while after the the In observed event. contrast, Figure 21 observed (green) and simulated (blue) time series at Croton (20a) and Sombra (20b). 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent sources, from ff 14266 14265 ected by ozone originating from di ff erent source than the Leamington maximum, with the former resulting from ff in the simulations. Leamington (LEA) stations ington (LEA) stations x Palmyra (Fig. 25d) shows a reasonable fit to the observations, though Palymyra Bear Creek station (25b) shows good agreement with the observed ozone; the tim- (25f) at this timeboth was southern being Detroit a and western Lake Erie, which may account for the multiple peaks the shoreline, pulls back (at 18:00peak UT), (absent then from comes ashore the (19:00 observationstions) UT). which The at third instead 21:30 model show UT/17:30 EDT constantover elevated and suggests concentra- on that the the norththe high observations side than concentration of in Lake ozone the St. generated simulation. Clair remains inmodel the values Bear lead Creek the areabiased longer observations about in 20 by ppbv about low. The 2 model h. surface maps The (25a, c, Leamington e) suggest model that values Leamington are and the locations of theeach three stations, station while are model shown and in observed Fig. ozone 25b, time d, series f. for ing, magnitude and shapes ofpeaks the (model first two 17:00 UT/13:00 peaks EDT arecorrespond and very to similar. 19:00 times UT/15:00 The when EDT first the respectively, model and Fig. predicts second 25a, the Lake c) St. Clair ozone maxima touches by NO 4.2.2 9 July: ozone transport event atFigure Bear 20 compares Creek observations to (BEA), model(Fig. values Palmyra 25), at Croton (PAL) comparisons and and are Sombraure stations; made here 25a, with c, three e additional shows stations model-predicted on ozone the and same wind-fields day. at Fig- 17:00, 19:00, 22:00 UT an hour. The modelhas simulations (24e) a suggest di that theemissions Sombra/Bear in Creek Detroit maximum creatingphotochemical ozone production over over Lake Lake Erie.is St. All biased Clair, three low time and in series the the suggest latter early that morning, the resulting model possibly from indicating excessively high ozone titration ima, though the model lags the observations for the location of the maximum by about wide) convergence zone. Thereasonable agreement time between series observations and comparison measurements for for the Leamington daytime (24f) max- shows a depicted. The modellocal accurately enhancement predicts of the ozone timingresponding between of to 14:30 the the and time main 15:00 when EDTthe the peak, of station convergence as about line in places the well 10–15 ppbv high model asshow cor- ozone simulation. the a immediately At over double Bear peak Creek inobservations (24d), the both by observations ozone about and maxima, 2 model h butservations the and show second is local peak of enhancements inthe lower of the model magnitude model predicts 1 than h ozone lags the leaving duration the the observations. of Lake 10 St. The Clair to ob- shoreline 20 in ppbv a at narrow times (10 when to 15 km Fig. 24. Theozone surface forming ozone along and a wind frontaltion, convergence maps line and (Fig. through another and 24a, lower north-eastby c, concentration of the e) feature Sombra end show sta- north-east of high ofmodel this concentration Leamington overpredicts sequence station high (24e). forms ozone The and time underpredicts series low for ozone Sombra during (24b) the shows 24 that h the interval put for cases of ozonewhere enhancement due these to features lake-breeze circulation, wouldtime noting impact, series the for stations then those comparing stations the at those model times. and4.2.1 observed ozone 8 July: ozone transport event at Sombra (SOM), BearModel-generated Creek surface (BEA), ozone Leam- and wind02:00, fields 04:00 p.m. at 17:00, local 18:00 time), and and 20:00 the UT time (01:00, series for the above stations are shown in The surface network describedthe earlier local can ozone be featureschemistry (which used the to interactions) model determine may suggests the beexamples are were extent occurring the taken to result by in which scanning of the through local the ambient circulation- model atmosphere. surface ozone and The wind field following out- 4.2 Local ozone events: detailed comparison to the surface network 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ect the hourly average ff ciently small to preclude plotting in several ffi 14268 14267 erence in the placement of the front is capable of ff erence between model and observations. The time ff ciently robust features that they a ffi Bear Creek (BEA), Croton (CRO), Sombra (SOM) and Grand Bend (GRB) ect on local ozone production. ff the lake-breeze fronts are su wind circulation over the lakes. shore of Lake Ontario.face Each divergence; of the these lakes(limits outflow in of from Fig. this this 28b outflowzones divergence also region persist contains region are through a indicated 04:00 perturbs p.m. region by (28c),tances the of dashed and inland. sur- the synoptic mauve outflow By lines). flow regions 08:00 pushdiscern; p.m. The considerable (28d) the convergence dis- average the wind impact speedlocations, of being probably the su indicating lake breezes significantsurface becomes variability divergence harder in to over the the duration lakes and by direction this of time the in the evening. The figure shows that ated with the lake-breeze frontsaverages appear of in the the surface afternoon.12:00 p.m., wind Figure 04:00 field 28 p.m., at shows andconvergence the 12:00, zones 08:00 23 (solid p.m. 16:00, mauve day local lines) 20:00 appearwest time). and on shore the 00:00 south UT of By west (08:00 Lake shore noon a.m., of St. (Fig. Lake Clair, Huron, 28b), the lake-breeze west and north shores of Lake Erie, and the north hours. In orderframe, to hourly determine model output the for impact thefor ozone of the concentration, these mass 23 tracking transient fields daysthat events and the of winds over lake-breeze a the fronts longer have intensivee a time were consistent average averaged diurnal by pattern, UT and a hour. significant 4.3.1 These averages UT show hour-average surface horizontal winds The synoptic flow is from the south-west during the intensive. Wind features associ- on the order of 150 km. 4.3 Averages of model fields: theThe average events impact described of above are transient transient events in that they may last over the course of a few convergence zones, and the transport of events created in these zones over distances lines (Fig. 27a, c, e)case is gives very good similar to evidence that for of the the mesoanalysis enhancement (27b, of d, ozone f). due Overall, this to lake-breeze frontal accounting for the concentration di series at Sombra stationthe (26d) same shows 1 a h very lagtion good in (26f) agreement the also with shows arrival a observations, ofabout very with the 10 good ppbv. maximum. agreement Both with The model observations,at model with and or a time observations below negative series at bias 80 at Croton ppbv, of vergence while Croton and zones Sombra Bear sta- and and Creek have Grand theozone maxima Bend, Lake concentrations. both St. in Clair/Detroit The the ozone pattern influence production of of region, the predicted con- have wind higher fields and frontal convergence an hour. Subsequent model concentrationscentration are fields biased (26 15 ppbv a, high c,on – f) the the show surface that south con- Grand side Bend ofthe is Lake front. on Huron, the with The edge a comparison ofshows rapid a to that change lake-breeze the the of front high mesoanalysis concentration concentrations in in atthe the the this Lake vicinity vicinity site Huron are of of front; strongly a Grand influenced 10–15 Bend by km the (Fig. di location 27) of In this example, highSt. ozone Clair concentrations and are are carriedozone generated to concentrations on the at the north-east to north 17:00,shown the in side 18:00, shores Fig. of of and 26a, Lake LakeCRO c, 19:00 Huron. and UT e. BEA) Model (13:00, are The surface shown 14:00, time inmodel-generated Fig. series wind 15:00 26b, EDT) for fields d, stations e, are (with and fromthe convergence g mesoanalysis north lines respectively. at and to Figure the 27 same gust south compares three fronts (GRB,at hours. the SOM, highlighted) Grand The model with Bend captures (26b), the high with concentrations a similar magnitude maxima that lags the observations by are due to the same sources as Leamington, advected4.2.3 further downwind. 10 July: transport of Detroit/Lake St. Clair ozone to Lake Huron, stations in the observations and simulated by the model. The model concentrations at Palmyra 5 5 20 25 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ect on local ozone production. ff 14270 14269 ect of the longer convergence lines discussed ff 45 ppbv) along the northern Lake Erie coastline and > erences in the circulation over each lake gives rise to their erences in the emissions databases for the two countries ff ff erences across the border suggest that accurate spatial allocation ect on the ozone production reaction; over Lake St. Clair (left side ff ff ects the ozone concentrations (29), that the Lakes are photochemical ff 30 km in diameter, and the Lake Erie source being relatively shallow ∼ cult to distinguish any e ciently strong to be present in the 23 day average wind fields (28), that ffi ffi ers between the two lakes. For Lake Erie, transport removes ozone in a thin ff erences in the vertical distribution of gas-phase ozone production. At 08:00 a.m. Figures 28 to 30 suggest that the local diurnal circulation associated with the two In order to examine the average ozone over Lakes St. Clair and Erie in more detail, The average Lake St. Clair surface ozone at 04:00 p.m. (29c) is clearly enhanced ff the updraft is now on the western shore of the lake itself. The land between the two has developed. Updraftsdriven over by the the Detroit north-west heathave shore formed island a of (“A” helical to Lake circulation “B”), withpollutants St. and the over Clair, synoptic downdrafts Lake flow, over likely and St. the may partially Lake lake Clair. allow (“B” a Erie, A recirculation to but of smaller “C”), the helicalThe larger recirculation wind size pattern barbs of occurs suggest aloft this thatsynoptic over wind some lake is air results roughly aloft in perpendicular mayair net also to over subsidence reach this Lake near cross-section, Lake Erie St. so thethe Clair the to surface. Lake opportunity (though reach St. the for Lake Clair the St. vertical Clair circulation may has be intensified small). and moved By southwards, 04:00 so p.m. that (Fig. 31b), (250 m altitude), but encompassing muchof of the simulated the 3-D S.W. side wind of fieldin through the Fig. the 31, Lake. 23 and A day shows cross-section averages howdi across di both lakes is shown (Fig. 31a), vertical winds are relatively light. By noon (31b), a strong vertical circulation is flanked by regionsLake of St. positive Clair ozone is transport.of larger transport The in is region horizontal not of extent, in transport suggesting the that plane removal of for at the leastLakes cross-section. some is of su direction this circulation a ozone production regions (30), thein Lake St. height Clair and source being a dome roughly 1500 m St. Clair source (left sidethan of that the over cross-section, Lake 30c) Eriephase has (right production a side rates much of greater are the(30d) vertical cross-section, di relatively extent 30c). high, The uplayer average to near local the gas- 5 ppbv/hour. surface, and The a narrow transport region pattern of ozone removal extending up to 1500 m production of ozone is the source of the high concentrations, but once again, the Lake more than 250 m above the surface. Figure 30c shows that gas-phase photochemical ozone feature in Fig. 29bClair matches convergence the line location of of Fig. the 28b. Lake Huron outflow andthe Lake St. 23 day averagewell 16:00 as UT ozone the concentrationsproduction corresponding and at loss cross-sections and the ozone of transport surfacehas ozone are over shown a concentration, in significant the Fig. 30a–d. ozone e lake, Theof gas-phase as size cross-sections, of 30b), each the lake region ofgreater enhanced than average 1500 ozone m, extends while to elevations the of enhanced ozone production over Lake Erie rises to no ever, it is di earlier, probably due to theirthough relatively some short features duration do and suggest highlyhanced their time-varying presence ozone positions, in concentrations the ( average.inland, Figure 29b matching shows the en- line of the convergence zone of Fig. 28b. A similar isolated high Lake Erie – this is(in due Canada, to shipping di emissionslines, in are the spatially US, allocated someErie). only shipping The along emissions large are the di of spread main shipping out emissions shipping over is essential the for southand forecasting that ozone side production those of over emissions the Lake may great have lakes, a significant e within the region of the lake-breeze convergence line and surface outflow (28c). How- Time-averaged surface ozone concentrations for thein same Fig. hours 29. as Fig. Theand 28 most are significant over shown high the concentrationFig. ozone region features 29c). shared are over by The Lake Detroit, former Erie, shows Windsor, higher and ozone Lake on St. the US Clair than (at on 04:00 p.m., the Canadian side of 4.3.2 UT hour-average ozone concentrations 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | cient ected ffi ff erences in the spatial ff ect on the average ozone. 20 ppbv. The photochemi- ff ciently robust features that ∼ ffi erences in ozone production between the ff 14272 14271 ected, while the elongated features in the frontal ff erence in the elevations of the ozone production regions ff The authors would like to acknowledge the financial support of Environ- ciently infrequent to have a less significant e ffi ) circulations explain the di measured in the vicinity of Toronto, Canada, Atmos. Environ., 9, 1137–1139, 1975. The statistical comparison with observations shows that the model forecast is sig- The results have important implications for ozone forecasting in this region. Cur- The main sources of emissions near Lake St. Clair are the cities of Detroit and Wind- re Anlauf, K. G., Lusis, M. A., Wiebe, H. A., and Stevens, R. D. S.: High ozone concentrations be possible, using the case-studiesand outlined here chemical to algorithms. gauge improvements to circulation Acknowledgements. ment Canada and the Ontariofully acknowledge Ministry the of assistance the of Environment the for AIRNow the program BAQS-Met and study. its We participating grate- stakeholders. References nificantly improved in goingparison from 15- to to the 2.5-kmperforms observations resolution. much show Shorter better a time thanmeasurements interval decrease on aloft. com- specific in days Further accuracy or improvements – for to specific the high resolution events, model particularly forecast on accuracy for average may the cal source regions overthe Lakes long-term St. average Clair ozonezones and are is Erie su a areCross-sections su of the 23-dayby average a wind vertical fields recirculation show thatozone may that concentrations enhance Lake result its St. from ozone strong production, Clairthese subsidence and features is suggests Lake over a that Erie’s the very high lake. local-scaleimpact The emissions on controls local ozone may nature concentrations have of in a significant this region. rent air pollutionoperate model on forecasts 15- generated and by 12-kmto resolutions, the adequately respectively. Canadian resolve These and thelations resolutions are performed US lake-breeze insu here circulations governments suggest –enhancements that of while these the the same regional high-resolution circulations ozone simu- may concentrations be by responsible for Surface convergence of the localand circulation the carries synoptic wind the thus ozone carries and the its ozone precursors much aloft further downwind. The simulations andozone formation comparisons over the with southern Greatlation observations Lakes and is photochemical significantly performed processing enhanced of by hereact precursors. local as circu- Lakes suggest photochemical Erie production and that St. regions,6 Clair with to frequently average 8 enhancements ppbv on performation the of hour order elongated by features of of early highkilometres, afternoon. concentration over ozone the extending The several course hundred lake-breeze ofemissions circulation source a regions, may day. and lead over These the to features photochemical the production originate regions downwind of of the Lakes. the urban includes emissions spread over thethe lake main on shipping the lane south on side the of north the side). border, while only on 5 Conclusions St. Clair. Thelarge Lake emission Erie region sources is onemitted heavily over the the influenced sourthern lake bystable shore itself, shipping marine and of emissions, boundary along Lake and layer itsdue the Erie. (which shoreline, to the is and relative These much are sizes emissions ofCanadian more trapped the and are within stable two US the lakes). than sides Di lake’s thatallocation of of of the the Lake emissions border St. data over forsides Clair each Lake country of Erie (Fig. Lake 30a, reflect Erie compare di north on versus the south east side of the panel; the emissions inventory, not shown, ( noted above (Fig. 30),al., and 2008). similar features have been noted in thesor; literature precursor (Levy concentrations et will be vertically distributed and re-circulated over Lake lakes has become an intense updraft, due to daytime surface heating. These vertical 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erences ff ce of Research and ffi , 2003. , N., Kottmeier, C., Lasry, ff 14274 14273 ´ enard, V., Hasel, M., Kaltho , C. J., White, A. B., Banta, R. M., Post, M. J., Brewer, W. A., ff shore sites in New England: Role of meteorology, J. Geophys. http://www.smoke-model.org/index.cfm ff ects of emissions data accuracy on particle sulphate predictions, ff ´ ethot, A., Patoine, A., Roch, M., and Staniforth, A.: The operational , C. J., Nielsen-Gammon, J., Darby, L. S., Ryerson, T. B., Alvarez, R. J., ff ries, H. E., and Tonnesen, S.: Sensitivity of ozone to model grid resolution – d, F., Ancellet, G., Arteta, J., Augustin, P., Bastin, P., Brut, A., Caccia, J. ı ff ¨ ´ enard, S. , Crevier, L.-P., Cousineau, S., and Venkatesh, S.: Cloud processing of gases ´ ries, H. 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G., Durand, P., Augustin, P., Bastin, S., Bonnefond, J.-M., B Lyons, W. A., Pielke, R. A., Tremback, C. J., Walko, R. L., Moon, D. A., and Keen, C. S.: Marchuk, G. I.: Methods of numerical mathematics, Springer-Verlag, New York, 316 pp., 1975. Lyons, W. A. and Olsson, L. E.: Detailed Mesometeorological Studies of Air Pollution Dispersion Makar, P. A., Gong, W., Mooney, C., Zhang, J., Davignon, D., Samaali, M., Moran, M. D., He, Lyons, W. A. and Cole, H. S.. Photochemical Oxidant Transport: Mesoscale Lake Breeze and Lyons, W. A. and Cole, H. S.: Fumigation and Plume Trapping on the Shores of Lake Michigan Makar, P. A., Moran, M. D., Zheng, Q., Cousineau, S., Sassi, M., Duhamel, A., Besner, Lu, R. and Turco, R. P.: Air Pollutant Transport in a Coastal Environment – II. Three-Dimensional Makar, P. A., Gravel, S., Chirkov, V., Strawbridge, K. B., Froude, F., Arnold, J., and Brook, J.: Logan, J. A.: An analysis of ozonesonde data for the troposphere: Recommendatioins for Li, S. M.: A concerted e Lyons, W. A., Keen, C. S., and Schuh, J. A.: Modeling mesoseale di Levy, I., Makar, P. A., Sills, D., Zhang, J., Hayden, K. L., Mihele, C., Narayan,Levy, J., I., and Dayan, Brook, U., J.: and Mahrer, Y.: A five-year study of coastal recirculation and its e Lemonsu, A., Pigeon, G., Masson, V., and Moppert, C.: Sea-town interactions over Marseille: Lemonsu, A., Bastin, S., Masson, V., and Drobinski, P.: Vertical structure of the urban boundary Lasry, F., Coll, I., and Buisson, E.: An insight into the formation of severe ozone episodes: 5 5 30 25 20 15 30 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | = 3 mean bias, NMB = root mean square error. = model mean, MB = daily mean Hourly O 3 d, F., Pigeon, G., Benech, B., and Serc¸a, D.: ı mod ¨ cient, RMSE 14277 14278 ffi correlation coe observed mean, M = east “BAQS Met” east “BAQS-Met” east“BAQS-Met” = R daily 1-h max O 3 obs O 0.46 0.44 0.49 0.44 0.43 0.39 0.46 0.33 0.60 0.61 0.63 0.61 42-km 15-km 42-km 15-km 42-km 15-km 42-km 15-km 42-km 15-km 42-km 15-km ¨ Evaluation statistics for 3 June 2007–31 August 2007, 42-km and 15-km AURAMS uck, B., Perna, R., Zhong, S., and Morris, G. A.: An analysis of the vertical structure of obs (ppbv)mod (ppbv) 56.9 65.2 57.7 63.5 55.6 64.0 57.9 63.6 32.6 43.6 33.3 40.0 31.7 42.9 33.6 40.0 33.0 43.8 33.7 40.3 32.1 43.1 34.0 40.2 Boston, 666 pp., 1988. centrations in southern Ontario, 1979–1985, Atmos. Environ., 22, 1161–1168, 1988. Landry, H.: Amodelling comparative systems, performance Atmos. evaluation Environ., of 43, 1059–1070, the 2009. AURAMS andOH-reactivity CMAQ of air volatile quality organication compounds of at air urban quality and42(33), model rural 7746–7756, predictions sites 2008. using across speciated canada: VOC Evalu- measurements, Atmos. Environ. the atmosphere and the upper-levelHouston, meteorology Texas, and J. their Geophys. impact Res. on D, 113(17), surface ozone D17315, levels doi:10.1029/2007JD009745, in 2008. in the southern Great LakesDiscuss., and in their preparation, influence 2010. during BAQS-Met2007, Atmos. Chem. Phys. Investigation on theRes., fine 74(1–4), structure 329–353, 2005. of sea-breeze during ESCOMPTE experiment, Atmos. L., and Vautard, R.: Ona the severe episode influence over of a meteorological coastal input area, on Atmos. photochemical Environ., modelling 41(30), of 6445–6464, 2007. Number of sitesM 1167 681 833RMSE (ppbv) 19.3 61 18.2 1167 18.3 681 18.1 833 16.0 61 13.2 15.3 1167 681 14.1 20.5 833 18.5 61 19.7 18.5 M MB (ppbv)NMBR 8.4 5.8 0.16 0.10 8.4 0.16 5.7 0.10 11.0 0.38 6.7 0.22 11.3 0.37 6.5 0.21 0.37 10.8 0.21 6.5 0.36 11.0 0.19 6.2 normalized mean bias, Yap, D., Ning, D. T., and Dong, W.: An assessment of source contributions to the ozone con- Stull, R. B.: An Introduction to Boundary Layer Meteorology, Kluwer Academic Publishers, Table 1. versus AIRNow. M Note: “42-km east” denotesMet” statistics denotes computed statistics for sites computed42-km: east 1167, for of 42-km sites 100 east: W within 833, within an 15-km: the 681, area continental 15-km 42-km bound “BAQS-Met”: domain; by region “BAQS- bounded 40.5–44.5 N by 40.5 and to 84–78 44.5 W. N Number and 78 of to stations: 84 W. Smyth, S. C., Jiang, W., Roth, H., Moran, M. D.,Stroud, Makar, C. P. A., A., Morneau, Yang, F., G., Bouchet, Makar, P. V. A., S., Moran, and M. D., Gong, W., Pabla, B., Zhang, J., et al.: Sills, D., Brook, J., Taylor, P., Zhang, J., Levy, I., Makar, P. A., and Hayden, K.: Lake breezes Rappengl Puygrenier, V., Lohou, F., Campistron, B., Sa 5 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2.83 0.132 − − 01010001 23 01 67 01 48 01 61 01 28 01 64 01 71 00 77 75 76 73 010101 939 0101 56 01 70 15 67 68 + + + + + + + + + + + + + + + + + daily 1-h min 3 0100 1.63E 00 1.11E 00 8.25E 00 1.30E 00 1.46E 01 1.47E 01 3.80E 01 4.02E 00 2.92E 00 1.29E 8.70E 0101 2.04E 01 3.84E 01 2.89E 01 3.70E 01 1.95E 1.91E + + + + + + + + + + + + + + + + + 1.93 0.031 − − 0100 1.18E 00 7.55E 00 5.87E 9.13E 0101 9.19E 01 2.50E 01 1.83E 00 1.86E 8.59E 0101 1.23E 01 1.27E 01 1.15E 01 1.49E 01 1.26E 1.39E + + + + + + + + + + + + + + + 1.20E-01 6.38E 6.89E-01 6.08E daily 1-h max O 1.60E 4.59E 4.23E 4.28E 3.79E 3.92E 2.70E 1.39E 3.94E 2.87E 3.70E 1.85E 1.65E − − Normalized Normalized Number − − − − − − − − − − − − − 3 01 00 00 00 0001 1.03E 01 01 00 6.17E 00 01 01 01 01 01 + + + + + + + + + + + + + + + 5.27E-02 4.81E-01 1.16E 3.12E 3.01E 3.01E 2.50E 1.78E 1.72E 8.42E 1.27E 1.15E 1.49E 1.20E 1.20E − − 3.78 − − − − − − − − − − − − − 0.090 − − 01 01 01 01 0101 6.45E 01 01 0101 4.09E 00 01 01 01 01 01 + + + + + + + + + + + + + + + + daily mean O 14280 14279 6.33E-02 3 2.07E 7.42E 1.21E 1.08E − − − − − 00 00 + + Slope Intercept Mean Bias Mean Bias Mean Error Mean Error of Points 0.63 0.60 0.57 0.60 3.77 1.78E-01 7.71E 5.51E-02 4.99E 2.02E-02 6.21E 0.092 − − − − − R 2.10E-01 4.27E-02 2.03E-02 − − − hourly averages O 3 zone statistics at all BAQS-Met surface mesonet stations, 2.5-km resolution simula- Statistical comparison between 2.5 km AURAMS simulation and aircraft ozone obser- obs (ppbv)mod (ppbv) 41.2 37.4 41.8 38.1 63.2 61.2 21.5 18.7 Number All Flights7 (06/26 12:34–15:06) 8 (06/26 17:20–19:04)9 7.40E-01 (06/26 20:10–22:20)10 (06/27 9.834E-01 12:30–13:42)11 (06/27 15:10–17:40)12 (07/03 22:44–07/04 13:00) 4.01E-0113 (07/07 08:18–11:16) 4.10E-0114 (07/07 3.84E-01 4.78E-01 2.73E-01 17:30–20:20) 15 (07/08 6.22E-01 5.77E-01 15:20–18:12) 1.00E 4.32E-0116 4.87E (07/08 22:20–07/09 1:00) 5.64E-01 2.67E 3.66E-01 1.24E 3.37E 3.97E-01 2.00E-01 7.33E-01 7.82E-01 1.85E 1.37E 1.48E Flight 1 (06/23 12:54–15:00)2 (06/23 17:22–19:56)3 (06/23 21:34–22:16)4 (06/25 14:38–17:24)5 (06/25 19:30–21:54) 6.65E-016 (06/25 23:00–06/26 0:00) 2.83E-01 9.82E-01 2.85E-01 4.17E-01 5.39E-01 2.76E-01 5.27E-01 1.18E 9.81E-01 1.42E 5.86E-01 1.81E R RMSE (ppbv) 17.6 13.2 17.9 13.2 NMB M MB M Statistic O Table 3. vations. Table 2. tions. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - 44 -

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monitoring stations used for (b) used for (b) ozone concentration, (c) ozone (c) ozone concentration, ozone (b) for used n; region east of 100W is “42-km-East”); (c) upward motion streamlines are streamlines in red, sketched motion upward the cross-section, superimposed on 20UT on superimposed the cross-section,

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(a) AURAMS 42-km, 15-km, and 2.5-km domains, (b) monitoring stations used for stations used for domains, (b) monitoring and 2.5-km 15-km, (a) AURAMS 42-km, Cross-section across Lakes of 3D wind fields Clair St. (8am), (b)_ and Erie at (a) 12UT 23 day average values at 20Z (4 pm local time): (a) (a) Clair St. Lake over ozone Surface time): local pm (4 20Z at values average day 23

surface winds. 16UT (12 noon), and (c) 20 UT (4pm). Net UT (4pm). 20 and (c) noon), 16UT (12 location of Inset: blue. in downward motion gas-phase production and loss, (d) ozone total transport transport total ozone (d) and loss, production gas-phase and Lake Erie, showing location of cross-section cross-section of location showing Erie, Lake and (31) (30) DRAFT – DO NOT DISTRIBUTE Figure 2: comparison observations (Mean Bias show to 42km (Mean Bias shown). comparison to observations used for 15-km sites monitoring GEM 15-km and 2.5-km domains and 2.5-km Figure 1: GEM 15-km DRAFT – DO NOT DISTRIBUTE AURAMS 42-km, 15-km, and 2.5-km domains, 4 5 1 2 3 4 2 3 5 6 7 8 1 1 9 GEM 15-km and 2.5-km domains. monitoring sites used for 15-km comparison to observations (Mean Bias shown). Fig. 2. (a) 42 km comparison to observations(c) (Mean Bias shown; region east of 100 W is “42-km-East”); Fig. 1. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - 46 -

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(ppbv). 3 : Observed and simulated O3 (ppbv), first 8 flights. first O3 (ppbv), : Observed and simulated Figure 4 (a-h) Locations of BAQS-Met surface Locations of BAQS-Met mesonet stations. DRAFT – DO NOT DISTRIBUTE Figure 3: 2 1 DRAFT – DO NOT DISTRIBUTE 1 2 3 Observed and simulated O Locations of BAQS-Met surface mesonet stations. Fig. 4. Fig. 3. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - 49 - Model-

(b) same as (b),

(c) - 48 -

, 18:06 to 18:32 UT, June 23. (b) Model- 23. UT, June 18:32 to , 18:06 1820 UT, June 23, 2007, (c) Same as 5(b), at (c) Same 2007, 1820 UT, June 23,

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1435 m a.s.l.), 18:20 UT, 23 June 2007,

∼ : Observed and simulated O3 (ppbv), remaining 8 flights. remaining (ppbv), O3 and simulated : Observed Figure 4 (i-p) Figure 4 DRAFT – DO NOT DISTRIBUTE 1700 m a.s.l.). (a) Model-predicted winds at 1010m agl (~1210m asl), (b) Model-predicted winds at Model-predicted asl), (b) (~1210m agl winds at 1010m (a) Model-predicted (a) Comparison of observed and model ozone and model of observed (a) Comparison 1 2 ∼ Comparison of observed and model ozone, 18:06 to 18:32 UT, 23 June. predicted ozone field at 1235m agl (~1435m asl), agl (~1435m predicted ozone field at 1235m asl). agl (~1700m 1500m Figure 6: asl). agl (~1435m 1235m DRAFT – DO NOT DISTRIBUTE Figure 5:

Continued. 1 2 3 4 5 6 7 8 9 predicted ozone field at 1235 m a.g.l. ( Fig. 5. (a) at 1500 m a.g.l. ( Fig. 4. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - 49 -

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model-predicted winds (b) , 18:06 to 18:32 UT, June 23. (b) Model- 23. UT, June 18:32 to , 18:06 1210 m a.s.l.), ong this section of the flight path, 18:00 path, 18:00 flight ong this section of the ∼ 1820 UT, June 23, 2007, (c) Same as 5(b), at (c) Same 2007, 1820 UT, June 23,

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Comparison of observed and modelled NO, flight 2 (ppbv). 2 (ppbv). NO, flight modelled and of observed Comparison Figure 8: 1435 m a.s.l.). (a) Model-predicted winds at 1010m agl (~1210m asl), (b) Model-predicted winds at (b) Model-predicted asl), (~1210m agl winds at 1010m (a) Model-predicted (a) Comparison of observed and model ozone of observed and model (a) Comparison ∼ Comparison of model and observed winds al of model Comparison Model-predicted winds at 1010 m a.g.l. ( predicted ozone field at 1235m agl (~1435m asl), agl (~1435m predicted ozone field at 1235m asl). agl (~1700m 1500m Figure 6: asl). agl (~1435m 1235m DRAFT – DO NOT DISTRIBUTE Figure 5:

Comparison of model and observed winds along this section of the flight path, 18:00 DRAFT – DO NOT DISTRIBUTE model output. output. model Figure 7: 1 2 3 4 5 6 7 8 9 5 6 3 4 1 2 Fig. 7. model output. Fig. 6. (a) at 1235 m a.g.l. ( Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - 50 -

- 51 - ong this section of the flight path, 18:00 path, 18:00 flight ong this section of the Model-simulated ozone profiles. (b)

14290 14289

(a) Observed ozone profiles from sondes, (b) Model-simulated ozone profiles. (b) Model-simulated ozone sondes, (a) Observed ozone profiles from Comparison of observed and modelled NO, flight 2 (ppbv). 2 (ppbv). NO, flight modelled and observed of Comparison Figure 9: DRAFT – DO NOT DISTRIBUTE

Figure 8: 1 2 3 4 Observed ozone profiles from sondes, Comparison of model and observed winds al and of model Comparison Comparison of observed and modelled NO, flight 2 (ppbv). Fig. 9. (a) Fig. 8. DRAFT – DO NOT DISTRIBUTE model output. output. model Figure 7: 5 6 3 4 1 2 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - 52 - - 53 -

along CRUISER driving 2 18:00 UT (02:00 p.m. local

(a) observed and model-simulated (b) at (a) 18UT (2pm local time), at (a) 18UT (2pm th tensive, (b) Observed and model-simulated model-simulated Observed and tensive, (b)

ved and simulated driving NO2 along CRUISER ved and simulated

14292 14291 observed and simulated NO

(c)

(a) CRUISER driving routes during the in during CRUISER routes driving (a) : Meso-analysis: lake-breeze front locations on June 26

DRAFT – DO NOT DISTRIBUTE Figure 10: Obser (c) driving routes, CRUISER ozone along routes. DRAFT – DO NOT DISTRIBUTE Figure 11 (b) 23 UT (7pm local time) local time) (b) 23 UT (7pm 1 2 3 4 CRUISER driving routes during the intensive, 3 1 2 23:00 UT (07:00 p.m. local time). Meso-analysis lake-breeze front locations on 26 June at (b) Fig. 11. ozone along CRUISER driving routes, time), routes. Fig. 10. (a) Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | As (c) Surface ozone (a) - 55 - - 54 -

23:00 UT (07:00 p.m. local (b) As in (b) but total transport rate of change (d)

18UT (2pm local time). (a) Surface ozone and (2pm 18UT nds along cross-section A-B of (14a); (c) As in cross-section A-B of (14a); nds along th 14294 14293

Gas-phase photochemical production and loss along (e) at (a) 18 UT (2 p.m. local time), (b) 23 UT (7 p.m. local time). Dashed local time). time), local (b) 23 UT (7 p.m. 18 UT (2 p.m. (a) at th 18:00 UT (02:00 p.m. local time), (b) m convergence pattern of 2.5-km resolution resolution pattern of 2.5-km from convergence inferred front locations Lake-breeze Model-predicted fields for June 26 Total transport rate of change along cross-section C–D. DRAFT – DO NOT DISTRIBUTE Figure 12: winds 26 on June model red lines: gust fronts; solid mauve lines: convergence lines. lines: convergence mauve fronts; solid gust red lines: DRAFT – DO NOT DISTRIBUTE Figure 13: wind barbs; (b) Vertical profile of ozone and wi Vertical profile of ozone wind barbs; (b) (b) but gas-phase photochemical production; (d) As in (b) but total transport rate of change of production; (d) As in (b) but total gas-phase photochemical (b) but cross- along production and loss Gas-phase A-B; (e) photochemical ozone along cross-section C-D. section C-D; (f) Total transport rate of change along cross-section Vertical profile of ozone and winds along cross-section A–B of (14a); (f) 4 5 1 2 3 6 1 2 3 4 5 (b) Lake-breeze front locations inferred from convergence pattern of 2.5-km resolution Model-predicted fields for 26 June 18:00 UT (02:00 p.m. local time). Fig. 13. and wind barbs; in (b) but gas-phase photochemical production; time). Dashed red lines: gust fronts; solid mauve lines: convergence lines. of ozone along cross-section A–B; cross-section C–D; Fig. 12. model winds on 26 June at Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (e) (b) - 57 - 18:00 UT and (d) Paquette Corners, - 56 -

(a) , at (a) Paquette Corners, (b) th concentrations and (e) 23 UT. at (d) 18UT

23UT (7pm local time). (7pm 23UT th 14296 14295

As in Figure 13, but for June 26 June for 13, but As in Figure Ozone comparison with surface observations, June 26 DRAFT – DO NOT DISTRIBUTE Figure 14: 2 1 Grand Bend. Model surface ozone concentrations at DRAFT – DO NOT DISTRIBUTE Figure 15: Bear Creek, (c) Grand Bend. Model surface ozone (c) 4 1 2 3 Ozone comparison with surface observations, 26 June, at As in Fig. 13, but for 26 June 23:00 UT (07:00 p.m. local time). Fig. 15. Bear Creek, 23:00 UT. Fig. 14. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Croton. - 59 - (b) - 58 -

Sombra, (a) , 17UT (1pm local time); (b) , 17UT (1pm th . (a) Sombra, (b) Croton. . th

14298 14297 rsus observations, July 8 observations, July rsus

(a) Meso-analysis on July 8 front locations lake-breeze Model-predicted ozone ve Model-predicted surface wind field and convergence zones. convergence zones. field and surface wind Model-predicted DRAFT – DO NOT DISTRIBUTE Figure 16: 3 1 2 DRAFT – DO NOT DISTRIBUTE Figure 17: 2 1 Meso-analysis lake-breeze front locations on 8 July, 17:00 UT (01:00 p.m. local Model-predicted surface wind field and convergence zones. Model-predicted ozone versus observations, 8 July. (b) Fig. 17. Fig. 16. (a) time); Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (a) Gas-phase (a) - 61 - - 60 -

total transport rate of change, (b) July 8th, 17UT (1 pm local time); (a) 17UT (1 pm July 8th, cross-section from cross-section Detroit to Toronto, North from

photochemical production, Lake Huron to Lake Huron to production, Lake photochemical , 17UT (1 pm local time). (a) Gas-phase (1 pm 17UT , th change, Lake Huron to Lake Erie cross-section. change, Lake Huron to 14300 14299 vertical cross-section from North Detroit to Toronto,

(b) gas-phase photochemical production, Lake Huron to Lake (c) Model-predicted fields for July 8 Model-predicted ozone and wind fields on wind and ozone Model-predicted total transport rate of change, Lake Huron to Lake Erie cross-section. photochemical production, Detroit to Toronto cross-section; (b) Total transport rate of change, Total (b) to Toronto cross-section; production, Detroit photochemical cross-section; (c) Gas-phase Detroit to Toronto transport rate of Erie cross-section; (d) Total DRAFT – DO NOT DISTRIBUTE Figure 19: DRAFT – DO NOT DISTRIBUTE

Figure 18: Surface concentrations (b) Vertical and wind fields; Lake Huron to Lake Erie. cross-section from (c) Vertical (d) 5 1 2 3 4 4 5 1 2 3 Model-predicted fields for 8 July, 17:00 UT (01:00 p.m. local time). Model-predicted ozone and wind fields on 8 July, 17:00 UT (01:00 p.m. local time); vertical cross-section from Lake Huron to Lake Erie. photochemical production, Detroit toDetroit Toronto to cross-section; Toronto cross-section; Erie cross-section; Fig. 19. Fig. 18. surface concentrations and wind fields; (c) Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Sombra. - 63 -

(b) - 62 -

Croton, (a) 17:00 UT (01:00 pm local (a) 22:00 UT (06:00 p.m.). SOM: , (a) 17UT (1 pm local , (a) 17UT (1 pm th (d) at (a) Croton, (b) Sombra. Sombra. (b) Croton, at (a) th Lambton Power-Plant. =

ozone concentrations, likely with associated measures are for the entiremeasures measurement intensive. 14302 14301

20:00 UT (04:00 p.m.); (c) Model-predicted surface ozone surface Model-predicted 9 for July fields and wind Model-predicted surface ozone and wind fields for July 9 Circled region identifies observed spike in local spike in identifies observed Circled region ozone created St. Clair. Statistical over Lake DRAFT – DO NOT DISTRIBUTE Figure 20: Figure 1 2 3 4 19:00 UT (03:00 p.m.); Model-predicted surface ozone and wind fields for 9 July at

time); (b) 19 UT (3 pm ); (c) 20 UT (4pm); (d) 22 UT (6pm). SOM: Sombra station. CRO: SOM: Sombra ); (c) (6pm). 20 UT (4pm); (d) 22 UT UT (3 pm time); (b) 19 Power-Plant P.P. = Lambton Lambton Croton station. DRAFT – DO NOT DISTRIBUTE Figure 21: Model-predicted surface ozone and wind fields for 9 July, (b) 4 5 1 2 3 Fig. 21. Circled region identifies observedozone created spike over in Lake local St.sive. ozone Clair. concentrations, Statistical measures likely are associated for with the entire measurement inten- time); Fig. 20. Sombra station. CRO: Croton station. Lambton P.P. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | model- (c) - 64 -

- 65 -

ce ozone and wind fields at 18, 22, 23 UT 23 UT 22, at 18, wind fields and ce ozone Lighthouse cove (LIG) and Leamington Leamington and cove (LIG) Lighthouse : model and observed ozone time series at Model-predicted wind fields and surface con- (f)

, (b) 14304 14303 (d) ,

(b) 20UT (a) Mesoanalysis, (b) Model-predicted wind fields and surface 20UT (a) Mesoanalysis, (b) Model-predicted wind fields and Mesoanalysis, th : model-generated surface ozone and wind fields at 18:00, 22:00, (a) . (a), (c), (e): Model-generated surfa Model-generated (c), (e): . (a), July 6 th (e) , Surface station Surface analysis (CRO), Croton at (c) DRAFT – DO NOT DISTRIBUTE Figure 23: convergence areas (with direction of winds at met stations as large arrows for clarity), (c) model- predicted gas-phase ozone production and loss. , (a) 4 1 2 3

DRAFT – DO NOT DISTRIBUTE Figure 22: Figure (14, 18, 19 EDT). (b), (d), (f): Model and observed ozone time and PAL series at CRO, LIG ozone time observed (f): Model and 19 EDT). (b), (d), (14, 18, stations.

stations, Julystations, 6 6 7 1 2 3 4 5 Surface station analysis at Croton (CRO), Lighthouse cove (LIG) and Leamington 6 July 20:00 UT Fig. 23. vergence areas (with direction of winds at met stations as large arrows for clarity), CRO, LIG and PAL stations. predicted gas-phase ozone production and loss. 23:00 UT (14:00, 18:00, 19:00 EDT). Fig. 22. stations, 6 July. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - 66 - - 67 -

ce ozone and wind fields at 17, 18, 20 UT 20 UT 18, 17, and wind fields at ce ozone : model and observed ozone time series at : model and observed ozone time series at

(f) (f)

, , l and observed ozone time series at BEA, PAL, and 14306 14305 (d) (d) nd observed ozone time at SOM, series ozone time nd observed and LEA BEA , ,

(b) (b) . (a), (c), (e): Model-generated surface ozone and wind fields at 17, 19, surface ozone and (e): Model-generated (a), (c), . th . (a), (c), (e): Model-generated surfa Model-generated (e): . (a), (c), : model-generated surface ozone and wind fields at 17:00, 19:00, : model-generated surface ozone and wind fields at 17:00, 18:00, th (e) (e) Surface station Surface (SOM), analysis Sombra at (LEA) Bear Creek and Leamington (BEA) Surface station analysis at Bear Creek (BEA), Palymyra (PAL) and Leamington , , (c) (c) , ,

DRAFT – DO NOT DISTRIBUTE Figure 25: (LEA) stations, July 9 22 UT (13, 15, 18 EDT). (b), (d), (f): Mode (b), (d), (f): 22 UT (13, 15, 18 EDT). LEA stations. DRAFT – DO NOT DISTRIBUTE Figure 24: Julystations, 8 (13, 14, 16 EDT). (b), (d), (f): Model a EDT). (b), (d), (13, 14, 16 Statistical stations. measures are for the intensive entire measurement period. (a) (a) 5 6 7 8 9 1 2 3 4 5 1 2 3 4 10 11 12 Surface station analysis at Sombra (SOM), Bear Creek (BEA) and Leamington (LEA) Surface station analysis at Bear Creek (BEA), Palymyra (PAL) and Leamington (LEA) BEA, PAL, and LEA stations. 22:00 UT (13:00, 15:00, 18:00 EDT). stations, 9 July. Fig. 25. SOM, BEA and LEAperiod. stations. Statistical measures are for the entire measurement intensive 20:00 UT (13:00, 14:00, 16:00 EDT). stations, 8 July. Fig. 24. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - 69 -

- 68 -

: model and observed ozone time (g) , (e) , : model-generated surface ozone at 17:00, (d) surface winds, convergence lines, and gust ,

(f)

. (a, b): 17UT. (c,d): 18UT. (e,f): 19UT. b): 17UT. (c,d): 18UT. (e,f): . (a, th , (b) 14308 14307 (c) Model and observed ozone time series at ozone time series Grand Bend observed Model and , . (a), (c), (f): Model-generated surface ozone at 17, 18, 19 at 17, 18, surface ozone (f): Model-generated . (a), (c),

th

, 10 July. (a, b): 17:00 UT. (c, d): 18:00 UT. (e,f): 19:00 (a) (b, d, f) Surface station Surface analysis and (CRO) Croton (SOM), Sombra Bend (GRB), at Grand Comparison between model-generated Comparison DRAFT – DO NOT DISTRIBUTE Figure 26: Figure Bear Creek (BEA) July 10 stations, UT (13, 14, 15 EDT). (b), (d), (e), (g): 15 EDT). (b), UT (13, 14, (GRB), Sombra (BEA) stations.and Bear Creek Croton (SOM), (CRO),

DRAFT – DO NOT DISTRIBUTE fronts (a, c, e) to mesoanalysis (b, d, f), July 10 fronts (a, c, e) to mesoanalysis Figure 27: 5 1 2 3 4 3 4 1 2 to mesoanalysis Surface station analysis at Grand Bend (GRB), Sombra (SOM), Croton (CRO) and Comparison between model-generated surface winds, convergence lines, and gust (a, c, e) UT. fronts Fig. 27. 18:00, 19:00 UT (13:00, 14:00, 15:00 EDT). Bear Creek (BEA) stations, 10 July. Fig. 26. series at Grand Bend (GRB), Sombra (SOM), Croton (CRO), and Bear Creek (BEA) stations. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 00:00 (d) 20:00 UT, (c) - 70 - - 71 -

16:00 UT, 20:00 UT, and (b) (c) 12:00 UT, 16:00 UT, (a) (b)

14310 14309 12:00 UT,

(a) 23 day average wind fields at (a) 12UT, (b) 16 UT, (c) 20 UT, and (d) 0 UT; 8 am, 12 am, 0 UT; 8 UT, and (d) 20 16 UT, (c) at (a) 12UT, (b) average wind fields day 23 23 day average ozone concentration fields at (a) 12UT, (b) 16 UT, (c) 20 UT, and (d) 20 UT, and at (a) 12UT, (b) 16 UT, (c) average ozone concentration fields day 23 DRAFT – DO NOT DISTRIBUTE Figure 29: respectively.pm, and 8 4 pm 12 pm, 0 UT; 8 am, DRAFT – DO NOT DISTRIBUTE Figure 28: of boundary lines, as regions marked solid mauve respectively. Convergence 8 pm, and 4 pm pm, with outflow regions divergence lines. dashed mauve marked 1 2 3 4 4 1 2 3 23 day average wind fields at 23 day average ozone concentration fields at 00:00 UT; 08:00 a.m., 12:00 p.m., 04:00 p.m. and 08:00 p.m., respectively. (d) Fig. 29. and Fig. 28. UT; 08:00 a.m.,marked 12:00 p.m., as 04:00 solid p.m.mauve mauve and lines. lines, 08:00 p.m., boundary respectively. of divergence Convergence outflow regions regions marked with dashed Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (c) - 72 -

12:00 UT (a) - 73 - ozone concentration, surface ozone over Lake (b) (a)

20:00 UT (04:00 p.m.). Net upward motion tion used for (b) ozone concentration, (c) ozone concentration, (c) ozone ozone (b) tion used for

(c) e cross-section, superimposed on 20UT surface on e cross-section, superimposed 14312 14311 ozone total transport.

(d)

Cross-section of 3D wind fields across Lakes St. Clair and Erie at (a) 12UT (8am), DRAFT – DO NOT DISTRIBUTE Figure 31: streamlines are sketched in red, Net upward motion (c) 20 UT (4pm). and noon), (b)_ 16UT (12 Inset: location of th blue. downward motion in winds. 5 1 2 3 4 16:00 UT (12:00 noon), and 23 day average values at 20Z (4 pm local ozone over Lake St. time): (a) Surface 23 day at 20Z (4 pm average values (b) Cross-section of 3-D wind fields across Lakes St. Clair and Erie at 23 day average values at 20 Z (04:00 p.m. local time): DRAFT – DO NOT DISTRIBUTE Figure 30: cross-sec of Erie, showing location Clair and Lake total transport. (d) ozone and loss, gas-phase production 4 1 2 3 Fig. 31. (08:00 a.m.), streamlines are sketched in red,superimposed downward on motion 20:00 in UT blue. surface Inset: winds. location of the cross-section, St. Clair and Lake Erie,ozone showing gas-phase location production of and cross-section loss, used for Fig. 30.