Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Chemistry and Physics Discussions Atmospheric were compared 2 and SO 2 levels of 23 % to 37 % at the urban 2 1 15178 15177 ´ exico, DF, Mexico , and G. Sosa and soot were compared with surface measurements 2 2,3 contribution to the 2 ´ oleo, 07730 M , L. T. Molina 1 WRF-Chem outputs of SO This discussion paper is/has beenand under Physics review (ACP). for Please the refer journal to Atmospheric the Chemistry corresponding final paper in ACP if available. Molina Center for Energy andDepartment the of Environment, La Earth, Jolla, Atmospheric CA, and USA Planetary Sciences, Massachusetts Institute of Instituto Mexicano del Petr gas industry. About 134 billion cubicto meters the (bcm) of World gas Bank were Global flared Gas in 2010 Flaring according Reduction Initiative (GGFR) estimates of flared and about 1 % attants to T2. the According three to supersitessurge the occurred event. on model, 23 the March, greatest which contribution coincides with of the both third pollu- cold 1 Introduction Flaring is an important sourceganic of Compounds greenhouse gases, (VOCs) particulate in matter both and upstream Volatile and Or- downstream operations in the oil and obtained at the threetribution supersites of of Tula MILAGRO flaringsupersite campaign. activities (T0), The to and results of the 29 suggest % totalpredicts to a low SO 39 contribution con- % at at the the suburban three supersite supersites, (T1). with For less soot, than the 1 model % at both T0 and T1; ide, soot andagainst sulfur measurements obtained dioxide. at Tula The asof part emission soot, of VOCs MILAGRO rates field and campaign. of COrates The of were rates NO the compared species with considered estimatesthe were obtained further chemical included by transport in IMP. The of WRF-Chempresents emission model the reliable to plume simulate performance from ofAbsolute 22 the Error March resolved to (MAE), meteorology, with 27 RootAgreement respect March Mean (IOA). to of Square the 2006. Error Mean The (RMSE), model vector RMSE and Index of This work presents a simulationHidalgo of Refinery the in plume emitted Mexico.with by The flaring a flame activities CFD of of combustionproducts a the of code Miguel representative interest in sour for air-quality: gas order acetylene, flare to ethylene, nitrogen is estimate oxides, modeled carbon emission monox- rates of combustion by- 2 3 Technology, Cambridge, MA, USA Received: 5 April 2012 – Accepted: 22Correspondence May to: 2012 G. – Sosa Published: ([email protected]) 14 June 2012 Published by Copernicus Publications on behalf of the European Geosciences Union. Abstract 1 Soot and SO supersites in the MILAGRO campaign from elevated flares in the TulaV. Refinery H. Almanza Atmos. Chem. Phys. Discuss., 12, 15177–15225,www.atmos-chem-phys-discuss.net/12/15177/2012/ 2012 doi:10.5194/acpd-12-15177-2012 © Author(s) 2012. CC Attribution 3.0 License. 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 1 − , reac- x ects clouds, slows ff eq emitted from flaring of natural 2 C and precipitation ranging from 432 to ◦ in the northern area of Mexico City that can 2 15180 15179 . The major industries of the city are located 2 ect to air quality and contribution to both global ff ´ on et al., 2001). According to current environmental , it is considered a short-lived climate forcer (SLCF) 2 erent flaring activities of PEMEX. ff et and Prather, 2009); since its atmospheric lifetime is short (days ff (Mo 2 eq global greenhouse gas emissions. In 2010 Mexico was the eleventh emitting 2 The Mexican Ministry of the Environment and Natural Resources (SEMARNAT) In Mexico, flaring operations are basically associated with activities of exploration, Black carbon (a component of soot) emissions from flaring facilities are of particular The composition of the gas to be flared depends on process operations. It may con- exceed the national air qualityest standard (0.13 emission ppm, inventory 24-h average). in According this to the region, lat- the emissions rates are about 323 000 tons yr and particulate matter (SEMARNAT-INE, 2006). brought the attention toto the Mexico Tula City area (60 for kmthe two NW); two main (2) major reasons: environmental industries (1) authoritieshigh in its of the levels relative the region of closeness State at pollutants of(RAMA) the registered Mexico stations beginning in were sued of the consequence 2006. Automatic ofbeen They their Atmospheric reported claimed emissions. Monitoring high that In concentrations the Network this of respect, SO the RAMA has industries include metal manufacturing,industrial processed waste. food, The emission chemical of and pollutantstries from incineration impacts combustion of processes the of regional thesefrom air indus- Mexico quality. In City addition, promotes the severefuentes inflow pollution et of al., problems 1994; untreated to Vazquez-Alarc sewage soilregulations, water and this water region resources is classified (Ci- as a critical area due to the high emissions of SO The city of Tulapopulation is of located nearly in 94semi-arid 000 the with inhabitants Mezquital average and Valley, in temperatures647 more mm, southwest of than increasing Hidalgo 17 140 from with industries.(TIC) north a The is to total region settled south. is within in In this an this region, area including region,Rios of the power the plant Miguel 400 km Tula (FPRPP), Hidalgo several Industrial cement Refinery Complex plants (MHR), and the limestone quarries. Francisco Other Perez minor focus on flaring operations isby twofold: (i) elevated to flares infer about on thepresent pollution contribution investigation of to levels; the di (ii) emissions to assess the1.1 viability to further Tula region extend the (Hidalgo State) during MILAGRO campaign (Molina et al., 2010). The motivation to Oaxaca states). In this work we focus on flaring emissions from the Tula refinery sions. Thus, control ofhave black immediate carbon benefits particles on by2011). air emission Therefore, quality reduction having and measures robust globalimproving estimates would warming emission of (Bond inventories emission et for air rates al., quality of 2011; modeling. soot UNEP, can beexploitation, helpful refining in and petrochemicalpany. These operations are of geographically PEMEX,ico located the (Tamaulipas, Veracruz in national and the oil Tabasco);Campeche eastern in com- sound), the coast and southeastern along in part the the of central Gulf region the of of country Mex- the (the country (Guanajuato, Hidalgo and convection and impacts the2011; hydrological Kahnert cycle et (Skeie al., etond 2011). In al., to terms 2011; CO of McMeeking globalto et warming weeks) al., potential, with black carbon(UNEP, respect 2011). is to This sec- feature CO promotes a rapid climate response when changing emis- tain heavier hydrocarbons, water vapor, hydrogenprincipally sulfide, nitrogen, (GE and Energy, carbon 2011). dioxide tive organic As gases a (ROG), polycyclic result, aromaticsoot hydrocarbons harmful are (PAHs), sulfur emitted by-products dioxide to and such the atmosphere. as NO interest because of theirand regional harmful climate change e (Chungreduces and Seinfeld, surface 2005). albedo It on can ice warm the surfaces atmosphere, accelerating snow melt, a of CO country with 2.5 bcm (World(EIA) Bank, estimates 2012). about The 17 milliongas US for metric Energy Mexico tons in Information of 2009 Administration (US CO EIA, 2012). volume from satellite data (GGFR, 2012). This represents up to 400 million metric tons 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 | 2 reported and NO 2 of PM and 2 1 − columns from 2 erences like flare designs, ff ; 22 671 tons yr x of NO 1 − obtained with a mobile mini-DOAS sys- cult to quantify due to the intrinsic fea- 2 ffi and soot. 2 emissions in the MCMA whereas the rest is 15182 15181 2 of CO; 44 265 tons yr 1 − ˜ neira and Edgar, 2008; Lawal et al., 2010), and field scale flares plumes of both the TIC and Popocatepetl volcano on the air quality of VOCs. 2 1 − ; 109 321 tons yr 2 The present work is related to the estimation of emission rates of combustion by- The paper is organized as follows: Sect. 2 presents the modeling procedure; Sect. 3 Other approaches to estimate emission rates include the application of stoichiome- Most estimates for regulatory purposes are based on a set of emission factors pub- The emissions from elevated flares are di This has motivated several research studies evaluating the influence of Tula emis- results and discussion, and finally the conclusions in Sect. 4. products released by agional sour impact gas of flare, flaring emissions in fromology order Tula for Refinery, to and nationwide to flaring obtain further activities. information The extendrates main this regarding objectives method- of the are: (a) primary re- to pollutants estimatewhich mass emitted flow handles by the a contribution of sourations soot gas in radiation; flare (b) Tula Refinery; with to model (c) asupersites; the to CFD plume and discuss combustion of (d) possible model flaring contribution oper- campaign to of regarding provide Tula the emissions plume complementary of to SO information MILAGRO for related studies in the lab-scale flares (Casti (Galant et al., 1984). Eachsidering in of their these methodology methods the provides physicalmore and estimates representative chemical rates. of aspects emissions of a by flare, con- thus yielding not handle intermediate speciesficult formed to in measure the combustion ororganic process to compounds, that estimate, sulfur are and compounds either which and dif- contribute nitrogen compounds to principally. air pollution,try such calculations as for volatile flaresal., in 2009); Nigeria the (Sonibare developmenttechniques and of for Akeredolu, quantification flares 2004; methods in Abdulkareem2011), based Houston and et on numerical and studies novel Canada with measurement Computational (Mellqvist Fluid et Dynamics al., (CFD) techniques 2010; to Johnson et al., lished by the Unitedrely States on environmental enclosed Protectiontrained Agency flares personnel (EPA). burning (Johnson However, these et landfillapplications al., gases and 2011). operating or Technological conditions di on canby introduce these estimates more factors uncertainty of (McEwen to plume the and estimates opacity Johnson, by 2011). In addition, these methodologies do to 30 %. Although heestimates reports of concentrations soot of emission combustion rates by-products, there in were his no work. tures of their operation;flame such position as by the high wind stacks, speed,characterized among strong the others flare heat (Gogolek emissions et radiation from al., two andin 2010). medium-height Strosher the oil Alberta (1996) field shifting for battery of flare both systems signed hydrocarbons and and mounted sulfur compounds. forfluorene were A this abundant sampling purpose. compounds system in Hefor was the sour reports, field de- solution gas flare; among flares. and others, Hydrogen that sulfide that tiophenes content were benzene in present the and sour gas ranged from 10 % and 4 April of 2006.of The model model correctly study captured with thefor column plume the measurements transport. TIC The supported plume. agreement However, the allevated estimates these flares, thus of studies the do SO apportionment notair consider of pollution explicitly one the remains of plume unknown. the of main el- emitters in the TIC to regional ence of the SO of the Mexico City Metropolitanin Area Rivera (MCMA). et They al.the used Ozone (2009) the Monitoring values together Instrument of with (OMI).contributed SO They satellite found about that retrievals one during of MILAGRO tenthroughly the vertical of half volcano SO local the and SO halfplume from from TIC. In TIC addition, with RiveraFPRPP. They et forward used al. particle average (2009) emissions also trajectories oftem. simulated considering SO They the represented both each the one MHR of them and with the a single stack and focused on 26 March of SO 44 632 tons yr sions on regional airal., quality, particularly 2009; in de Mexico Foy et City (Querol al., et 2006). al., For 2008; instance, de Rivera et Foy et al. (2009a) analyzed the influ- 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 | mix (2) (1) τ is the density of ρ , the reactive volume fraction -th species, at top boundary. This value is κ j 1 − is the chemical reaction time and c τ j RR , is scaled by κ and the turbulent dissipation rate. The reader j 15184 15183 ff + e RR µ ! i j e Y at ground to 5 m s ∂χ ∂ (Open Field Operation And Manipulation) version 1.5 1 ff − e ® µ ective dynamic viscosity. is the mass fraction of the ff

j i e Y is the residence time; ∂ ∂χ res τ = is the e  ff j e e Y µ i mix e u τ c ρ τ +  + c i τ ∂ res + ∂χ τ + res j τ e Y Currently, data of the gas stream is scarce; however we set a composition based In this expression, The PaSR model splits the computational cell into a reacting and a no reacting zones. The reactingFoam solver is used in this work to model the flame of the representative In Eq. (1) the bar denotes a time-averaged value whereas the tilde represents a = ρ ∂t ∂ 83 species and 512 elementarythe reactions organized formation in of 11 both mechanisms, sulfur which and includes nitrogen oxides. based on measurements conducted atThe Tula left during side MILAGRO of campaign thefor (IMP, domain 2006c). velocity is and a temperature. Dirichlet The boundary bottomopen boundary with boundaries. is the a same non-slip values wall. as Right the and profiles top are on information provided by PEMEX.gas, We hydrogen are sulfide, considering methane andtively. to The nitrogen represent Glassman with natural chemical mass mechanismsince is fractions it used of considers to reactions 0.7, solve of the 0.2, post-combustion combustion gases and (Glassmann, chemistry, 0.1 2008). It respec- considers crosswind conditions. The computational domainwith is a dimensions 2-D of structuredof 1600 hexahedral m mesh the wide domain. andImposed The 500 profiles m mesh of high. is pressure, TheThe finer temperature flare velocity near and varied is velocity the from are located flare used 0 at in m as s the order initial center to conditions. refine the flame region. The flame of the flare corresponds to an unconfined non-premixed combustion under which takes a value from 0 to 1. Itκ is calculated as: is the mixing time whichis depends referred on to the references for further details. 2.1.1 reactingFoam solver set-up With this approach, mass exchangeposition. with The the chemical reaction source zone term, drives the change in com- (PaSR) (Nordin, 2001; D’Errico etequation al., that 2007; handles Marzouk and thespecies Huckaby, turbulence-chemistry 2010). the model A interaction solves, transport together is with used the equations for of each mass, momentum chemical and energy: ization application (OpenFOAM 1.5 user guide). sour gas flare. It isdetailed a transient chemical code mechanisms that to solvesal., model the Navier-Stokes the 2007). equations. mixed-controlled It It combustion can (D’Errico use is et based on the Chalmers Partially Stirred Reactor combustion model Favre-averaged quantity. the mixture and library designed for continuum mechanicsand applications Huckaby, 2010; (Kassem Weller et et al., al., 1998).Aside 2011; It Marzouk from can handle combustion unstructured polyhedralible applications, meshes. and it compressible flows, includes heatFOAM solvers transfer 1.5 and for user electromagnetics multiphase, among guide). incompress- othersand It open (Open- is source capable meshing software, of intoeral converting its numerical meshes native schemes meshing for constructed format. the in It temporal,the commercial also gradient, post-processing, divergence includes and sev- results laplacian can terms. For be visualized with ParaView, an open source visual- 2.1 Combustion model The CFD toolbox OpenFOAM is used to simulate the combustion part of this work. It is an open source finite volume 2 Models description 5 5 25 20 15 10 15 20 25 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (4) (3) ), surface β , in non-premixed n resolution were used for ), coagulation ( ◦ γ , α er and Seaman, 1990) was used ff is the Avogadro’s number. The reader o N ox R 3 15186 15185 / 2 ) 100 nodes with 35 vertical levels (Fig. 1a). The v , and particle number density, f v × s f ρ ( 3 / ) as they apply to the balance between transport and 1 ox n R 3 / 1 erent aerosol and photolysis schemes. 2  ff  2 π nudging in the PBL and in the lower ten levels as well, for wind, s o n ρ ff N 36   β − − δ α + in order to save computing time. In this step we used the Grell-Devenyi ) and oxidation ( = denotes soot particulate density and ff γ γn s  ρ o = n N v f t s  Four-dimensional data assimilation (FDDA) (Stau The model was run in concurrent mode for the first two domains with the chemistry A representative simulation for a flare was performed; the results obtained in con- In this work, acetylene is taken as the nucleation specie, since the nucleation rate Soot was calculated with the phenomenological model of Moss (Moss et al., 1995). d ρ t d d d the third domain. The chemistry of the plume was solved in the third domain. to nudge meteorology during the firsting 24 was h applied of the for simulationit the period. is first Only analysis better two nudg- to domains.temperature turn After and o sensitivity water tests vapor mixing (not ratio. shown) we found turned o scheme for the convective parameterizationthe (Grell second and domain Devenyi, were 2002). used The for results boundary for and initial conditions in an hourly basis for et al., 2006), thethe Monin-Obukov RRTM model (Mlawer for et the al., surfaceand 1997) layer shortwave and (Skamarock radiation Dudhia respectively. et (Dudhia, The 1989) al.,domain gravity schemes 2005), wave only. for drag Six the option longwave hourly isinitial used and Global for lateral Final the boundary first Analysis conditions. data with 1 A 6-day simulation period, fromwas 00:00 conducted UTC 22 using March00:00 three UTC to on 00:00 domains UTC 20 in 27 Marchare March one-way with of 27, nesting two 2006 9 days configuration. and ofparameterizations It 3 spin-up. used km The started in each grid at this with1983; cell Chen work sizes 100 and for include Sun, the 2002), the thethe domains NOAH Purdue Yonsei Land University Lin Surface Model (YSU) microphysics (Chen scheme (Lin and Dudhia, for et 2001), the al., Planetary Boundary Layer (PBL) (Hong (Grell et al., 2005).teorological It component preserves when solving thechemistry, the transport, it transport includes grid di in and sub-grid physics scales. schemes Aside of from2.2.1 the the me- WRF-Chem set-up 2005) developed at the National Oceanic and Atmospheric Administration (NOAA) WRF-Chem version 3.2.1 is usedfully for coupled the air to quality the simulation. It Weather is Research a and chemistry model Forecasting (WRF) model (Skamarock, The mass flow of thecriterion pollutants for was placing estimated the withrepresent slice far-field a was conditions. slice to method consider (see low Sect. values 3). of The thejunction OH with radical the in air orderpaper quality dealing to model with are this used regard to is under further preparation refine2.2 (Almanza the and combustion Sosa, model. 2012). Air A quality model of the model is(Brookes and assumed Moss, to 1999). Flame beal., radiation in 1996; is calculated proportion Morvan with et to theas al., P1 the implemented 1998). model local by (Sazhin The concentration et D’Errico In-Situ of Adaptive et acetylene Tabulation al. (ISAT) (Pope, (2007), 1997), is used to speed up the computing time. is referred to the references forrates, further parameters details and regarding derivation. the expressions of the reaction where It includes simplified termsgrowth describing ( the nucleationproduction ( of soot volume fraction, flames. 5 5 25 15 20 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 erent species at ff following the work of Zhang et al. (2009), erent heights with respect to the tip of the ff ff 15188 15187 erence between the inflow and outflow along the slice. . are more variable suggesting an increase in the domain ◦ ff 2 concentration increases at lower temperatures. However, the 2 and CO 2 Nevertheless, the combustion chemical mechanism is more accurate at high tem- Our results indicate that the variation of the mass flow rate depends on the location The second approach (E2) considered the average magnitude and average direction The mass flow was calculated with two approaches. In the first one (E1), the product Since we are focusing only on the flaring emissions in this study, we did not use the WRF-Chem was run with the Regional Acid Deposition Model version 2 (RADM2) possibly that soot can belevels oxidized are in about the two atmosphere. timesconditions, In those addition, since of at NO NO. this This distancelevels NO can of support both the SO height assumption and of hence far a flame longer simulation time. peratures, so that inherentregions, inaccuracies mainly are related with present the in cooling the of estimates species as in they the are far transported. flame region in which flaring sootthe is flame, in OH far-field conditions. andlevels As soot are shown levels higher in are Table than 1,the relatively those at comparable flame, 30 of m in we OH from magnitude. butimportant, considered At still since that 38 the comparable m, the levels in soot are influence magnitude. two At of orders of 60 the m magnitude atmospheric above higher than chemistry those could for OH, be and quadrant. For each time intervalfraction the was product multiplied with of these thefinal average profiles values mass between and flow density then and for numericallycalculated mass integrated. both values The approaches at was each time obtained interval with for the the arithmetic last sixof mean seconds the of of slice. all simulation For the time. thisrepresent work the conditions we of are the measurements interestedthe by in Rivera plume et the al. downwind region (2009), of far which from considered the the point flame sources. in OH order levels to are estimated to infer about the and as a result, the contributionrate in was each calculated of by the the four quadrants di was computed. The mass of the velocity alongnot the change slice. significantly Since the the average values number of of direction, inflow which regions always was were small, in this the first did account for the inflow through the slice. The resulting profile was integrated numerically of density and mass fractionthe with slice. the velocity It was considered done in the a direction point-by-point basis of along the velocity vector in each point in order to The results of thein 2-D Fig. simulation of 2 thefive and sour slices. Table gas These 1. flare slices Thesimulated in are flame. table a located The shows cross mass at wind mass flowvelocity di are and was flow species computed presented estimates mass with fraction 500 ofslice average fields. points at di These of intervals points the of were 0.1 mixture sampled s, density, for for each the last 6 s of simulation time (Fig. 2). 3 Results and discussion 3.1 Combustion model 3.1.1 Sour Gas Flare Doran et al. (2008),default and values computed Li by et the model.ity al. Zhang of (2010). and forecast Dubey The concentrations (2009), using initial reportwas the calculated and small default as sensitiv- boundary profiles. suggested Plume conditions in riseassumes Beychok are a of (1995), the tilted the which flame considers flaring the by plume 45 flame length and national emission inventory; therefore no other emission was set for WRF-Chem. chemical mechanism (Stockwell et al., 1990;the Chang Modal et Aerosol al., dynamics 1989) forModel for the Europe (MADE/SORGAM) gas coupled mechanism phase and with forSchell the the Secondary aerosol et phase Organic al., Aerosol (Ackermann 2001),Cumulus et together parameterization al., with 1998; was the turned FAST-J o (Wild et al., 2000) photolysis scheme. 5 5 25 15 20 10 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | to for 1 and 1 − − 1 . This − 2 . Since IMPei 1 − estimate of IMPei is ciency of flares, and for the main peak of ffi 2.5 2 ects the results, the in- ff erence of 0.97 kg s ff emitted from F2 is half of F1, and 2 , the rate with E1 is high. 2 15190 15189 and CO. The rates were obtained with the two . This represents a di 2 1 − and the upper limit of RdF is 0.36 kg s . The reported emission of NO 1 2 − to 4.03 kg s 1 it is clear that sulfur and carbon are not present in a comparable − 2 . , VOCs, soot, CO 2 x , the estimate from this work is higher than IMPei but in agreement estimates for just one flare, it is not possible to infer which flare emits x x , NO and CO 2 2 with respect to IMPei. The range of the estimates is related to the approach , both lower than the reported peak value and in agreement with the limits 1 1 − − mass flow rates obtained with the combustion model are higher than the IMPei 2 at TIC. It is possible that this could be related with process variations, but at the , soot and CO 2 2 Regarding NO Even though the approach of calculating the mass flow a This highlights the relevance of including flame-wind interaction in the estimation of The results also suggest to increase simulation time and to refine the mesh down- SO On the other hand, the estimates are comparable with the RdF reported value. The Even though the rates obtained with the combustion model are high, these can be The high variability in the stream composition of each flare can be shown with the IM- fluence of the chemical mechanism of the combustion model is important. Currently it with RdF with respect26 to March is NO aboutreports 0.614 kg only s NO more quantity, so we assumereason, equal we values compare of with the estimate RdF0.23 kg for estimate. s the The three emission flares. rateof For ranges RdF this from estimate. However, 0.14 similar kg s to SO position and velocity of thetions stream also sent contribute to to thesulfide the flare concentration. are uncertainty In important, of addition, so the the thatthat estimates. 2-D our can This assump- domain imply be lacks to the obtainedtransient lower dynamics and in hydrogen and steady a flame state. width 3-D setup. Work is in progress to account for this in both same time, variations in the wind fields could have contributed. emissions from flaring sources. Itall is in possible that the this calculation interaction method was of not the considered IMPei. at wind the combustion plume.flame For are instance, slowly eddies dissipated.promotes generated a They after slower present transport the relatively of ignition high these of eddies concentration by the of the SO crosswind flow. Besides, the com- variation in emission oftion the of sources wind in is important, thetherefore since region. increase it In pollutant can the emissions. diminishreported case Perhaps the by of Rivera combustion this et flares, e was al. theSO (2009) captured contribu- on in 26 the March of main 2006 peak which was about 12.47 kg s high variability on the fluxes when acquiring measurements, and associate them to considered representative for Tula Refinery. For instance, Rivera et al. (2009) reports that F3 emitsranges about from a 2.91 kg s gram.2.15 With kg s this informationused the to compute estimate the mass for flow. the three flares rates of this work arehowever, the in rate agreement with with E1 theof approach confidence the is interval RdF relatively of estimate, high. the which It includes measurements; all is the similar emission to sources the in average TIC, value including FPRPP. used to compare the modeledcan soot be estimate. The attributed variations to inoperation the plants. the Unfortunately composition Refinery there stream configuration, are since no measurements each in flare this isestimate respect. related for to F1. specific IMPei roughly suggests that SO sion inventory IMPei conductedmeasurements by by the Rivera IMP et al. inall (2009). the Since species TIC the for IMPei (IMP the does 2006a,SO not three b), contain flares, information as the of well estimated as total the mass flow ratePei. is For SO available only for quantity in all flares. Thisis is an reflected order in of the amount magnitude of between emitted F1 particles. and Roughly, F3. there Currently the PM The estimates of massmodel flow are presented rates in for Table 2. flaringspecies: It shows SO emissions the rates obtained at with farapproaches field the conditions discussed for combustion in the following the previous section. The table lists information of an emis- 3.1.2 Emission rates of primary species 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 | . 1 − usion ff with an 7 kg h 1 − ± ect thermal NO ff ect soot formation. ff of HONO is estimated. 1 − (Table 2). Since the IMPei method does is estimated. Despite the flaring stream 1 − 1 in Eq. (3). It assumes oxidation only by O − ox 15192 15191 R can diminish the soot extent by generating OH radicals (Glass- for the three flares, assuming high content of elemental carbon in er at these facilities, the calculated emission is comparable in mag- 3 1 ff − erences with reported emission rates, the estimates of this work are ff kg s 5 − 10 × is slightly lower. From the IMPei estimates, practically all the contribution is from 2 It is pertinent to mention that other important species for atmospheric chemistry can IMPei suggested emission rate is 1.07 g s CO is about 2 times higher than IMPei. With respect to the estimates at S5 slice, Despite the di Johnson et al. (2011) developed the Sky-LOSA technique, an in-situ method to quan- Soot mass flow is lower than IMPei estimate. IMPei valuesConsidering suggest only that methane F3 for is the fuel stream can underestimate the soot gener- As for VOCs, we obtained a lower value than the IMPei estimate. Since the chemical be calculated with thepurpose combustion of model, this even work.formaldehyde though at For Mont they instance, Belvieu, are in Parrish the notIn et Houston related this al. Galveston Bay with work (2012) facilities, of the an reportcomposition 17 can emission primary di rate emissions of of nitude. In 11.3 kg addition, h Li et al.morning (2010) photochemistry reports of the the importance MCMA. of In nitrous this acid work (HONO) 0.74 in kg the h considered in the composition of this work. comparable with respect toemissions measurements inventory. reported by Rivera et al. (2009), and IMP flare at Uzbekistan hasflares. a diameter of 1.05 m, about twonot times consider the the diameter chemicalcan of interaction be MHR among lower, because species, of it the is influence of possible sulfur that contentCO this on estimate soot oxidation. F3. This can beof attributed to F1 the and stream F2 composition. It can suggests present that elevated the hydrogen gas content; stream however this specie was not flare at a gasuncertainty plant of 33 in %. Uzbekistan According toover, and Figure their 1 determined estimate of an their is paper, averagewe the representative rate flare obtained for is of a the visibly 2 sooty. soot overfire g More- s comparable region emission in rate of magnitude on the with the flame. the overfire In Sky-LOSA region our estimate. of work, However, the the simulation aforementioned of 1.07 g/s, tify mass emission rates of soot from flares. They applied the method on a large-scale Moreover, the influence of sulfurtion in step, the since flame chemistry SO mann, can 2008). be This important could in influenceit the the is oxida- location possible of that theIn the slice addition, in combined far the presence field original of conditions.et values nitrogen Thus, al. of and (1995) soot sulfur report model a flames. that parameters In model are parameters this used are work, inThis sensitive this perhaps is to work. being the the studied Moss parameters kind in are of the sensitive fuel corresponding paper in to (Almanza di the and presence Sosa, 2012). of sulfur. ated in the flame,soot (Richter since and this Howard, 2000; hydrocarbon Woolleymodel et has al., for 2009). the soot The tendency Nagle-Strickland-Constable oxidationradical; to was however produce used OH for low radical levels can of be relevant in the oxidation step (Puri et al., 1994). mechanism only considers hydrocarbonstake up into to account C3, higherinclusive, it hydrocarbons because is the present computing not in time possible the could at be real prohibitive. this stream, stage like5.2 to C4, times C5 higher than oris F2 C6 8.01 and 11 timesthe higher IMPei than particulate F1. estimation. Considering this, our estimate represent natural gas, so thatsions. fuel However, NO it formation is isconditions. excluded possible In to addition, that contribute the prompt to presencein the NO of the emis- formation sulfur flame in could because theformation contribute it stream (Alzueta in can complicates et al., the influence fuel-rich 2001). dynamics the oxidation of the fuel and a only includes a sub-mechanism for thermal NO formation. Methane is considered to 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 | C ◦ and 1 − erence ff C for the con- ◦ ´ an (EAC), Merced C. The IOA is greater cient for wind direction ◦ in all but CHA, TAH and ffi 1 − , and with an IOA of 0.82. 1 − in all stations, except in TPN where 1 − 15194 15193 ), wind speed (WS) at 10 m above ground and wind T respectively. The IOA for TPN, VIF and XAL of 0.53, 1 − . With respect to the IOA, the model resolved wind direction more 1 − and 2.72 m s . In general RMSEvec range from 2 to 3 m s 1 1 . According to these authors the correlation coe − − 1 − Aside from the inherent variability in the parameterizations employed by WRF, pos- On the other hand, the model captured relatively well the dynamics of temperature at Fast et al. (2009) report reasonable predictions of the wind fields at CHA station for Surface temperature presents MAE and RMSE slightly greater than 2 The performance was evaluated at the MCMA and at the three MILAGRO supersites. monitoring equipment is even less than the first mass level of the model. Nevertheless, accurately at T2. Thisapparently value had is the very lowest similar performance.lower Nevertheless, to than the T1 those RMSEvec with is of 0.81. 2.61 T1 m However, and s at T2. T0 thesible model reasons for thethe inaccuracy vertical in resolution the of performance theabove of grid, surface. the since In model the this first can respect,50 level Zhang be m in since et attributed this their al. to work higher (2009) is resolutioncan seems located within give to higher the about wind place boundary 50 speeds m the layer with is respect first around to level surface 10 below observations to since 100 the m. height This of the the three supersites, with slightlyand better the performance IOA at is T0. greaterbehavior The than MAE at 0.9 is T0, in less all withFor than the the 2 both sites. other sites, The MAE the model andMAE performance better less was RMSE captured than slightly 2 wind about better m s speed at 1 m T2 s with an IOA of 0.76 and a the period from 6 March towork 30 March. the They IOA used FDDA for withhad wind observation inaccuracies speed nudging. In at and our XAL direction andof is VIF the relatively because high the gap model for flow.night tended this Moreover, in to station. the stations over-predict near They downslope the the also flows extent westernis side in obtained of in their the our basin simulation work rim,a at not except TAC moderately and in propagated IOA TAH CUA. with for at Similar low wind behavior IOA direction. for wind direction and at CUA with of 2.68 m s at TPN was higher thanstations at is TAH. In obtained. this Nevertheless, work theywork a modeled focuses similar the only behavior whole after of 22 MILAGRO the period March IOA as and for mentioned this the in same Sect. 2.2.1. highest RMSE these authors report corresponds for wind speed at TPN with a value speed are comparable with those reported by Zhang and Dubey (2009). In addition, the or equal than 0.9speed in presents all MAE stations, and exceptit RMSE in close XAL is to where 2.20 m 2 it s m0.69 s is and 0.88. 0.70 In respectively, suggests a thatenough similar accuracy, the particularly way, model at wind is TPN. In notwith this capturing sense, 3.93 the m the s dynamics RMSEvec is with alsoTPN higher where at TPN is highestrather as low previously in mentioned. some Although of the theless stations, than IOA especially 0.86 for at in wind TAH most with direction of 0.54, them. is it However, is the greater values of than RMSE 0.7 for and temperature and wind Villa de las Flores (VIF) andcan Xalostoc be (XAL). found A in more (Zhang detailedstations and description are Dubey, of 2009) presented the and in stations (Tie Table et 3. al., Table 4 2007). shows Results the forsidered performance the at MCMA stations, the except supersites. in MER, PLA and XAL with almost 3 temperature at 2 m above grounddirection ( (WD). With respect to(RMSEvec) is the calculated. wind This field, statistic considers the1995). both RMSE speed of and direction the errors vector (Fast, wind di In the basin, representativestations monitoring stations were of Chapingo RAMA(MER) (CHA), Plateros were (PLA), selected. Cuajimpalpa Tacuba (TAC), Tlahuac The (CUA), (TAH), Tlalnepatla surface (TLA), ENEP-Acatl Tlalpan (TPN), The performance ofdomain, the is meteorological assessed fieldsSquared by obtained Error means (RMSE) with and of the WRF-chem Indexand the of in Matsuura, Agreement Mean 2005). (IOA) the (Willmott The Absolute et third model al., Error surface 1985; variables (MAE), Willmot considered the for this Root purpose are Mean the 3.2 Air quality model performance 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 | 4 H lev- 2 2 and C 2 H 2 , CO, C x ects of Sierra de Guadalupe . As with soot, the estimates x ff , soot, NO 2 . This allows the emission rate to be in , but in the latter study observations were 1 ff − 15196 15195 at T0 and T1 are used to compare the results of and NO was used for F3, and considered 30 % for the three flares. This was accomplished by 2 2 2 are equal for the three flares. All of the emissions are held 4 H 2 and C 2 the same estimate of NO H 2 x 2 ects are not well captured (Doran et al., 2009) and can influence the modeled ff On 24 March, a northeasterly component prevented the plume to be transported to At T0, the model suggests a contribution after midnight on 22 March until 05:00 LT. For NO Although the statistics suggest improvement in the model set-up, the meteorological the basin and practically there was no contribution at T0. The model suggests that the crease after this hour. However, therethe were results missing data suggest in that thistogether period it with to is confirm stability related it, conditions. but westerly with As component, topographic the the e plume model wasthe observations. further captured Although transported the the timing by evolutionwas of the along important the north- to peak the capture was day relatively slightlyin well underpredicted, as a the nudging more showed phase accurate of by timing. the Accordingels observations to by peaks, the the reflecting model, plume the of greatestpractically contribution TIC spent in occurred most SO of on the this day day. It in is the basin. important to mention that the plume ond peak that alsofields started show at a southerly 05:00 LT. component Itentire that plume is transported left related the T0 with plumethe early local to day, on sources the and this north since the day. so thethe On plume that 23 gradual wind reached the increase March T0 northerly of again the winds in observations prevailed most the after of 02:00 early and morning. until The 07:00, model with captured a small de- strain the total emissionsetting rate the of emission SO raterelative agreement to with roughly measurements 3model. kg without Surface s measurements losing of generality SO withthe model the (Fig. combustion 3). There was a northerly windwith on a the strong previous lateral day transport that from transported the the east plume after at midnight. this Measurements site, show a sec- constant in all the simulation period. 3.3.1 SO Given the overestimation obtained with the combustion model, it was decided to con- of both C 30 % less for F1 and F2 was considered, similar to NO Tula Refinery (Fig. 1b).are Only considered as the inputs estimates tosince WRF-Chem. of acetylene The SO is latter important two hydrocarbons toin were soot methane considered formation rich and combustion ethylene (Law,for is 2006). inputs an to Table important 5 WRF-Chem. by-product presents the mass rates considered less for F1 andFor F2. soot This the ensures same the value of values the to estimate be was in set agreement equally with for the measurements. three flares. With CO, fields can be considered reliablefor for the this surface study wind given field the together moderately high with values the of performance3.3 IOA of surface temperature. Flaring plume transport This section presents the WRF-Chem simulations of the plume by flaring activities at our work covers the(Fast last et two cold al., surge 2007).riod. events These (NORTE2 Since add and no more NORTE3) convectivethis described variability parameterization work, in was to this included the could for dynamicsal. have the contributed of (2009b) innermost to turned the domain the it simulation in accuracyal. on, pe- (2010) of whereas and the Zhang Doran model et andassimilated as al. Dubey into (2008) well. (2009), the turned De Zhang model it Foy et o as et previously al. mentioned. (2009), Li et pact in the performance ofmal their e simulations. Moreover, the localwind topographic direction and at ther- the surface.satellite In remote addition, sensing de data Foy forto et the improve al. land the (2009b) surface model employ model performance. high and It resolution without is data worth assimilation to mention that the simulation period in Li et al. (2010), also place the first level of the model at around 50 m without visible im- 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 ff erences ff erence is related ff erences for 23 March, ff erences in concentration ff erence between the two scenarios ff levels, since the diurnal cycle is not as visible 15198 15197 2 for the three flares. It corresponds to the rate ob- 1 − levels as shown by observations is correctly captured by 2 levels at T0 on this day. to 1.97 kg s 2 2 ects. at night are lower than on 25 March, because a southerly component levels was calculated for the simulation period. Results are presented in ff 2 2 obtained with the combustion model is high, the di erence at T1 on 23 March can be attributed to variations in the wind fields and ff 2 De Foy et al. (2009a) present impact fractions in the MCMA by emissions from TIC With these two scenarios, the average contribution of flaring emissions from MHR to In order to infer about the influence of the emission rate on the modeled concen- This mechanism was also important in early hours of 27 March. At these hours, At T1 the behavior is similar in all the simulation period. The main di The recirculation was present in the early morning of 25 March until a northerly flow 23 % at T0 andof 29 % about at 14 % T1.2.22 This at ppb yields and T0 1.42 a and ppb global at 10 T0.for di % At each at T1 emission a T1. rate. concentration of The 2.02 ppb corresponding and average 1.48 ppb concentration isfor obtained is the of whole MILAGRO campaign. Theyconfigurations are in about their 40 % model to set-up.emissions 57 This %, can suggests according impact the to more di possibilitythat than of on local periods 23 sources. when March, According emissions TIC from to MHR our contributed results, more it than local is sources possible to the total topographic e the total SO Table 6. When using theat higher T0 emission and rate 39 estimate % the at contribution T1. is With about the 37 % lower emission estimate, the average contribution is the contribution is fromparticularly flare in F1. the Results afternoon, suggestday of maximum was about di also 4 ppb reproducedhavior at as was T0 in and obtained the 27 for ppb previousare the at simulation, 7 time ppb T1. and series. at The in T0 For peakof general and the for SO the 8 other this ppb same days at be- the T1.levels are maximum These relatively values di low suggest in the thathigh whole even di simulation though period the at estimate both supersites. The relatively then T0. This reflects in the timing of thetration peaks in values the at observations. theemission supersites, rate of a SO similartained simulation with E2, was in conducted agreement with by both lowering IMPei the and RdF, and was assumed that most of 23 and 25 March the model captured the transport of the plume first reaching T1 and was important for SO nearby Tula, there wasthe flow plume from further both to the theThe gradual southeast north, decrease supporting and of the southwest SO the increment that model. of transported emissions by recirculation. to the influence of localas sources at on T0. SO Nevertheless, measured values are about two times greater than at T0. On day. 26 March presentstion a before similar midday behavior, and withlevels with of the a SO contribution late mostlyremoved northerly by most flow of recircula- in the thelater plume form afternoon. before the midnight. Nevertheless, northeast However, the winds transported from the the plume northwest back to and the basin, so that recirculation Nevertheless the model did notwithout capture reaching this since the the basin. plumethe De moved strength farther Foy of to et the the al.also down-valley west (2009a) flow from the from attributed northeast, the this which northeast, to totally and subtle change the changes the up-valley resulting in flowgradually plume transported to transport. the Tula plume backreached to T0 the after basin. midday. Observations The show modelis no suggests clear in that peak the relative after plume midday, agreement but the with model the dynamics of the measurements for the rest of this of a residual massthe of measurements show the two plume23 peaks located March, along at from the the 08:00to day western to with the 21:00 side higher first LT. A of concentration peak23 peak the than at March was basin. on T0. peaks measured However, It with at is a T1 possible similar with that evolution a this were similar was registered timing a at contribution both from T0 Tula, and since T1 on (Fig. 3). small peak at 19:00 is originated by downslope flow that promoted the recirculation 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 | 1 − erences ff obtained by the IMP 2.5 15200 15199 applies for soot. 2 erence can be attributed to the influence of local sources. ff and other species, the time series between these species present di 2 levels at T0. However, it is important to note that we did not include the urban erence in the timings between the plume of TIC and the peaks from observations. ff 2 As the plume continued to be transported, it reached T1 at 09:00. In the early morn- The plume reached T0 at 10:00, with the peak at 11:00. As at T1, there was southerly This can be observed with more clarity on 23 March. On this day the model suggests At T1 a similar contribution of local sources is also present, but with lower magnitude. Because we did not include the national emission inventory, the diurnal variation at At T0 it is evident the influence of local sources, since the maximum modeled con- The predicted concentrations of EC at T1 are compared with observations in Fig. 4. It Another simulation was conducted using estimates of PM flow. The peak from the plume coincides roughly with the minimum of the observations, ing, the surface fields suggest thatdeveloping southerly from wind the was present north at06:00. later T1 Therefore, with in it a the is gradual morning. possible flow sources, that In the and contrast, peak that the of TIC observed the emissions observations peak were can more was be important at related before toflow midday. local at this site inIn the the early model, morning however, with thebasin, slope slope flow since flow from the is the IOA moderately western forThe captured side wind gradual near of direction the the decrease is basin. NW around in side 0.7 the of for the EAC, observations TAC, and from TLA 08:00 (Table 1). can be attributed to northerly a transport from T2started to to T1 develop and to ended T0. atishing, At 13:00. and The T2 model the the captured timing observations this of peak,value show its the was that gradual maximum overpredicted dimin- after value and 04:00, at the a 05:00 peak LST. peak ended However, the earlier, concentration at about 11:00. frequent so that diurnal patternsplumes are from not nearby as sources pronounced are ascontribution more in of important the other the (Fast sites, et plume and al.,observations from dilute 2009). at TIC This this could implies site. present that Thus,a a a the di similar influence timing of with localFor the sources instance, at peak on T0 of and 22 EC while T1 March the can the model induce main peak is peak around of midnight. observations at T0 is at about 06:00 LT, the frequency and intensity ofal., fires 2007). diminished considerably with the NORTE3 (Fast et For instance, the emissions from thebe highway important connecting Mexico (Fast City et and al., Pachuca 2007). can Because T2 is a remote site, daily variations are more of Fig. 1 in their paper biomass burning sources close to T0. However, after 23 March centration is comparable to low background levels. Fast et al. (2009) show in panel (d) and used the threeare stacks shown for in the Fig. 5. flares to represent allT0 the and MHR T1 is emissions. not Results captured.possible Instead, contribution the from modeled TIC time in seriesthere reveals EC were the levels small days at with contributions most theafter after three midnight 24 sites. in March, According all to mostearly the the in of sites model, the the on afternoon. 22 contributions March. possibly In occurred contrast, late in the morning and reason for such a di (IMP, 2006b). The emissionMHR rate and considered FPRPP. The all purposevated the flares to possible is include combustion to other determine sourcesfor sources if both for FPRPP dilution of and is soot MHR. relevant. Similar rather The to than mass de Foy rate just et was ele- al. set (2009a), to we set 0.23 kg one s stack for FPRPP mental carbon at the three supersiteset obtained al., during 2010) were the used MILAGRO campaign towith compare (Molina SO model results. Although soot isin transported the together local dynamics. The meteorologicalof fields the are discussion similar of for SO both species so that part can be noted that thethan modeled observations. concentration is Aside about from three the orders of inherent magnitude uncertainty lower of the estimate, one possible emissions in this study. 3.3.2 Soot transport Elemental carbon (EC) is considered to represent soot. Surface measurements of ele- SO 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 | for 3 − we took 2 a et al. (2009), ı ´ MHR emissions. For SO + 15202 15201 time series, it is possible that on 24 March a 2 . Then we count the number of hours in which this threshold 2 . In contrast, the plume directly impacts T1 first and later T0. The 2 the contribution of flaring activities at TIC to the total soot levels was 2 A contribution plot was constructed in order to infer about the possible surface impact The figure shows the time, as percent of hours for the simulation period,The that spatial the distribution is similar to that reported by Zambrano Garc When considering the total emissions of the power plant and the refinery, more than Figure 6 presents the plume from TIC on 23 March at 12:00, for the considered air As with SO Fast et al. (2009), report considerable underestimation of EC at T0 and T1 in the Although the plume can dilute as it is transported, EC levels are comparable in order On 26 March the model suggests a contribution from early morning until midday at The model shows that the plume impacted the three sites on 25 March and 26 March. with a tendency of transport towards the northeast. It can be noted that for primary was selected. It wasis performed based by on taking the asoot detection threshold limits and value of 1 ppb the forwas for measuring each exceeded SO instruments. pollutant, in We all which set the simulation 0.01 µg period. m The plot isflaring shown plume in spent Fig. in 7. representativenarios locations for soot within are this the region.the overfire The rates rate considered obtained and the with sce- FPRPP E1 and E2 approach of the slice method. pollutants. It shows the transportrology. of the plume under the influence ofof complex the meteo- TIC flaring plume. An area encompassing most of the Tula region and the basin corresponds to slice S0 in Table 1. Results are presentedhalf in of Table 6. the total levelsthan at 10 % T2 can at be T0.influence attributed At of to the T1, TIC slice the inof location contribution the for magnitude is simulation estimating period, roughly higher the and double whenflame soot less of region. mass taking These T0 flow the results in rate support overfireconcentration is all the levels. region, about scenarios. importance an than of The order local when sources considering on predicting the soot far combustion model emissionlocal rate sources estimate, is are rather more feasible important. and thus theestimated. In contribution order of toperformed complement the by contribution means estimation of another taking simulation the was mass rate at the overfire region of the flame. This that it is about 68 times lower. This suggests that low values of EC, obtained with the son, if we take the IMP estimate for flares and compare it with the total of TIC, it implies the morning; at T2 after midday, and no visible contributionperiod at from T0 05:00 to before 10:00. 17:00. Inthe our period work, after the 05:00 model until suggestsit contribution 10:00 by was inclusive, TIC on clearer at 23, on T1 25, in aqueous 23 26, March. and reactions, 27 However, possible since March. scavenging Nevertheless, atby by this Doran precipitation stage et al. the on (2008), model rainy can is days be not relevant. as considering suggested of magnitude when taking into account all the combustion sources at TIC. For this rea- discussed for SO observations minimum value atAccording T0 to is calendar, close this to daysince the corresponds there model to were Sunday. maximum, This no like reflects sharpand on in peaks T1 23 the in are March. time the clearer series morning. on The this influence day. of On local 27 sources March, at there T0 was a slight contribution at T1 in tions indicate small valuesnot at correctly that captured hour. It and isT0 the the possible possible model that contribution peak the occurred coincides timing23 earlier. with of Nevertheless, March. the at the Local minimum plume of sources thesites. was could observations contribute at to 14:00, the similar to peaks before the plumeT1. reached Later the at T2,In the this timing case, of most of the the model modeled peak levels agrees of EC with at the this observations site at are 14:00. due to a recirculation as TIC. Similar to thecontribution form discussion Tula was of not SO captured by the model. The behavior is similar ontions 25 at March 09:00. at T2, However with at the T1 peak the from model the suggest model and a observa- peak at midday, but the observa- suggesting that around midday of 23 March part of the EC levels at T0 came from 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 | 2 2 is . 2 1 − and soot. kg s 2 2 − compared to 10 1 , which is within − 1 × − 8.10 ± are in the range of es- 1 − 2 10 × and NO 2 , and further input them to WRF-Chem. ® levels is about 37 % at T0 and 39 % at T1. 2 15204 15203 erent locations with respect to the tip of the flame. erence with the IMP emission factor ranged from ff ff by the measurements. The calculated rate for NO 1 , which is of the same magnitude. Moreover, the overfire − 1 − , CO and soot were obtained with the combustion model. 2 , the di 2 according to the estimation method (E1 or E2). , SO 1 x − 3.80 kg s the highest calculated rate of this work is 2.73 kg s and the measurements suggest 2.77 ± 2 1 , NO − 4 H 2 kg s 2 of the emission factor by the IMP. However, when taking the overfire slice, it to 1.4 kg s − ,C 1 1 2 − − 10 H 2 × The results from the present study suggest a more feasible contribution of TIC in SO These results complement previous findings of studies related to TIC conducted by The impact of these emissions on the air quality of MILAGRO supersites was further On the other hand, the emission rates for SO Several slices were placed at di Since the flares operate continuously, there exists the potential of a constant expo- to infer about the contribution ofMCMA flaring and activities near to the levels refinery. of secondary pollutants in the levels on 23 March in mostwith of a the basin, potential with contribution similarcontribution behavior on of on 24 25 elevated March March flares of according toThe 2006, to total and high SO measurements contribution The valuesbasin estimated can on be 23 March.This attributed information torecovery can of the support the persistence related gas studies of in regarding the the the refinery. plume possible in the other research groups, and at the same time it gives the possibility to extend this study model peaks with observationfurther peaks in improvement some is days recommended, ofels the particularly within simulation the the period. PBL, refinement However, perhaps to to of perform consider the warm convective vertical starts parameterization for lev- periods in of the days inner instead of domain a and continuous run. the range of 4.90 6.88 evaluated for the period from 22Given March the to relatively 27 good March of valuesof 2006, of WRF-Chem focusing MAE, on was RMSE, SO reliable RMSEvec enough andMILAGRO to IOA, supersites. the compare Analysis performance results nudging withtiming surface was when measurements the important at plume to reached capture the relatively three well supersites, given the the relative agreement of et al. (2011). As0.6 kg s for SO timates obtained withal. measurements (2009). For during SO the MILAGRO campaign by Rivera et estimate was comparable to the Sky-LOSA estimate of a large-scale flare by Johnson 2.63 g s yielded a rate of about 1 g s The emission rates of primaryflare pollutants in were a estimated 2-D for configuration.atmospheric a The chemistry. representative model The sour allows gas the masslar, quantification flow C of was species obtained relevant for withThis a model takes slice into method.tent account In of the particu- hydrogen cross sulfide, windmethodologies. important interaction with aspects the not flame considered and at the all con- byWhen emission considering factors the far flame slice, soot emission is about 60 mg s This work presents simulationsTula Miguel of Hidalgo the Refinery, plumeat in emitted the order by MILAGRO to the supersites. study threeof This the elevated combustion was by-products flares contribution accomplished with of of by OpenFOAM flaring calculating emissions mass flow rates sure, even though the concentrationinformation is when small. considering These contribution theformation plots emission can for inventory, give and exposure further may inand provide specific population. supporting regions in- which can include vegetation, crops, soils 4 Conclusions plot suggests that theimplies plume spent that more the time northflaring at operations. T0 region However, when than considering of at thethe the soot the emissions plume other basin of can FPRPP supersites. was and spread This MHR, thepresents farther a to most similar the exposed behavior. south to of emissions the from basin for this simulation period. SO pollutants the distribution is similar, but it can change for secondary pollutants. The 5 5 25 15 20 10 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 − shore flares in Campeche Sound , 2011. ff erence between observed and modeled ff ˜ nor et al., 2003). 15206 15205 doi:10.5194/acp-11-1505-2011 The authors thank Tommaso Lucchini for his help with the soot code, usion flames, Combust. Flame, 116, 486–503, 1999. ff 9644588-0-2., 1995. forcing by black carbonPhys., and 11, organic 1505–1525, matter with the Specific Forcingturbulent Pulse, jet Atmos. di Chem. preparation, 2012. Combust. Flame, 127, 2234–2251, 2001. Modal aerosol dynamics model forron., Europe: 32, development 2981–2999, and 1998. first applications, Atmos. Envi- from gas flaring: a1004–1015, case 2009. study of oil producing area of Nigeria, Energ. Source. Part A, 31, Although this work focused on Tula Refinery, it is feasible to apply these tools to a For the simulation period of this study, the flaring plume spent more time at T0 than The combustion model requires further improvement, particularly in selecting the Results showed a transport of emissions from T2 to T1 toThe T0 estimated on contribution 23 of March, flares when to total soot levels is sensitive to the location As for soot, the model suggests that the flaring plume has less influence at the su- Bond, T. C., Zarzycki, C., Flanner, M. G., and Koch, D. M.: Quantifying immediate radiative Beychok, M. R.: Fundamentals of Stack Gas Dispersion, Third Edition, Ch. 11,Brookes, ISBN S. J. 0- and Moss, J. B.: Predictions of soot anf thermal radiation properties in confined Alzueta, M. U., Bilbao, R., and Glarborg, P.:Inhibition and sensitization of fuel oxidation by SO2, Almanza, V. H. and Sosa, G.: Numerical estimation of the emissions of an industrial flare, in Ackermann, I. J., Hass, H., Memmesheimer, M., Ebel, A., Binkowski, F. S., and Shankar, U.: Acknowledgements. Georg Grell for hisMPICH comments and regarding Guohui WRF-Chem, Li Ed fordata Scott his of Wilson support the Garcia with MILAGRO WRF-Chem. for campaign In his is addition, help greatly the with acknowledged. use of the experimental References Abdulkareem, A. S., Odigure, J. O., and Abenge, S.,: Predictive model for pollutant dispersion magnitude to the measurements by Parrish et al. (2012). country-wide analysis of theextend impact the of modeling flaring activities ofpreviously in conducted air by Mexico. quality the For IMP instance, emissions (Villase it of can o formaldehyde, a highly reactive organic compound (HRVOC), and which was of similar as a separate result, it was possible to suggest a first estimate of nitrous acid and at the other supersites.exposure This to implies TIC that pollutants, which the isthat north in when region agreement considering with of previous emissions the studies.south of basin It region also the can of showed power have the more plant,tants basin. the can When plume be considering included can the to reach emission complete part inventory, the secondary of analysis. pollu- the location of the slicebe and helpful the gas for stream delimiting composition. the The combustion estimates emissions of by this the work can flares of MHR. Moreover, of the slice inagreement the with combustion IMP model. emission As0.14 factors % stated and at above, this T0, overfire resulted estimate 0.3possible in % led emission a at sources to suggested T1, at better contribution and7 TIC, %, of including 1.02 17 % % the at and power 59 T2. plant, % Nevertheless, the at T0, when contribution T1 is considering and about all T2 the respectively. cluded, this could haveconcentration contributed of to soot. the Even di thoughfor urban results locations suggest near flare theand emissions MCMA, rural they are can areas not exert near significant a the greater refinery. contribution to both urban meteorology favored northeasterly windsAt due T2 to the the model presence peaks agrees of relatively the well third with cold observations. surge. persites, compared to localare feasible sources. at Concentration the supersites valuesof as of FPRPP well EC and as in MHR less the wereremained, than basin. considered so When 1 into µg all m the that the model,in combustion background the sources almost concentration contribution all of was local the higher sources simulation than period. Since model the concentrations national emission inventory was not in- 5 5 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ´ arez, , 2008. usion flames to predict nez, A.-P., Ruiz-Su ı doi:10.5194/acp-9-9599- ´ ff files/downloads/GE%20Flare% doi:10.5194/acp-8-1377-2008 , 2007. usion package with an explicit treatment ff , 2009. , 2009b. , 2011, last access: June 2012. 15208 15207 ney, J., de Gouw, J., Doran, J. C., Emmons, L., Hodzic, ff z-Palacios, G., Bennett, S., and Peasey, A.: Epidemiological ı ´ , 2006. , 2002. doi:10.5194/acp-7-2233-2007 doi:10.5194/acp-9-6191-2009 http://www.ge-energy.com/content/multimedia/ doi:10.5194/acp-9-4419-2009 , 2009a. ciency of high momentum jet turbulent combustion flames, J. Environ. 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M., Wang, W., and Pow- SEMARNAT-INE, Secretaria del Medio Ambiente y Recursos Naturales/Instituto Nacional de Sazhin, S. S., Sazhina, E. M., Faltsi-Saravelou, O., and Wild, P.: The P-1 model for thermal 5 5 30 20 25 15 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | x erent heights ff 3.808.10E-2 6.88E-2 2.73 4.69E-2 1.97 ± ± . 1 − 15214 15213 4.39 4.50 3.58 3.37 2.73 15.53 14.50 10.06 9.22 8.57 3.83E-2 5.46E-2 9.15E-2 8.98E-2 6.88E-2 S1 (0 m) S2 (4 m) S3 (30 m) S4 (38 m) S5 (61 m) ). F1, F2, and F3 stands for Flare number 1, 2 and 3 respectively. RdF –– – – 4.07E-3 – – – 2.77E-1 – 1.05E-01 7.31E-2 1 F1 F2 F3 Total TIC E1 E2 − 1.31 6.17E-1 9.57E-3 1.94 4.90 2 2 2 9.43E-3 1.73E-1 8.27 8.45 – 8.57 7.90 SpeciesSO NONO Soot 9.74E-2CO 9.46E-2CO 1.07E-3OH 5.25E-2 9.26E-4 1.86E-1 Slice 8.90E-5 1.61E-1 4.51E-2 4.1E-2 9.20E-2 8.62E-5 3.70E-2 2.65E-2 9.75E-2 6.11E-5 7.78E-4 1.08E-1 1.03E-5 9.14E-7 Summary of the mass flow rates of combustion air pollutants. Units are in kilograms Mass flow rates obtained with the E1 approach of the slice method at di /Soot 2.35E-4 5.03E-4 2.63E-3 3.37E-3 – 6.11E-05 6.26E-05 2 2 x 2.5 2 SO CO CO – – 6.23E-2 – – 1.08E-01 2.07E-01 NO NO VOCsPM – – 2.44E-1 – – 2.33E-02 2.38E-02 Species IMPei* RdF This work represents the combined referenceemissions. E1 of and Rivera E2 et refer to al. approach (2009) 1 and and 2 de of Foy the slice et method al. respectively. (2009a). * SO per second (kg s Table 2. Table 1. in the flare simulation domain.of The the capital slice. S The and number thethe in simulated number flame. at parenthesis All the shows the right the estimates represent height are the of in number the kg s slice with respect to the tip of Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | WD WD 3.652.683.93 0.54 2.95 0.71 3.24 0.63 0.70 0.62 3.802.992.29 0.86 2.45 0.75 2.22 0.72 2.21 0.75 0.81 0.68 3.6 0.88 2.613.38 0.57 0.81 RMSEvec IOA RMSEvec IOA WS WS 1.721.56 2.290.97 2.00 0.86 0.98 1.31 0.82 1.05 1.34 0.80 0.82 1.40 0.80 1.51 1.07 0.76 1.02 2.01 0.85 2.20 1.35 0.81 1.32 2.72 0.84 1.39 1.75 0.53 2.13 0.69 0.70 MAE RMSE IOA 0.9 1.23 0.82 1.871.86 2.62 2.44 0.69 0.76 15216 15215 MAE RMSE IOA T T MAE RMSE IOA MAE RMSE IOA Station T0T1T2 1.22 1.79 1.72 1.84 2.25 0.94 2.29 0.93 0.91 Model Performance at MILAGRO supersites. Performance statistics of the surface variables in the third simulation domain. Location TLA (NW)TPN (SW) 1.93VIF (NE) 1.67 2.21XAL (NE) 2.14 1.29 0.93 2.51 0.90 1.66 2.82 0.96 0.88 CHA (NE) 1.64 1.96 0.94 CUA (SW)EAC (NW) 1.61MER (C) 1.90 2.00PLA (SW) 2.27 2.17TAC (NW) 0.91 2.00TAH (SE) 0.91 1.68 2.63 2.40 2.04 0.90 2.09 0.90 2.34 0.92 0.91 Station Table 4. Table 3. with respect to the center of the city is below the station name. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | T2 –––– % Avg 59 0.25 0.071.02 2.73E-4 3.92E-3 and soot levels at MILA- 2 T1 . 3 − % Avg 3929 2.02 17 1.48 0.25 0.3 4.50E-3 0.03 4.19E-4 15218 15217 F1 F2 F3 2.01 0.94 0.01 % Avg 5.39E-2 5.39E-28.00E-2 7.70E-2 8.00E-21.38E-2 1.10E-1 1.99E-4 1.38E-2 1.99E-4 1.38E-2 1.99E-4 2 4 2 x 2 H H 2 2 Species FlareSO emission rate NO NONO CO 2.76E-2C 2.76E-2C 3.95E-2 9.00E-2Soot 9.00E-2 1.10E-1 6.93E-5 6.93E-5 6.93E-5 MHR 7 0.29 + units are ppb and soot units are µg m 2 High emission 37 2.22 Low emissionoverfire 23 1.42 0.14 6.12E-3 Far flame estimate 0.01 4.64E-4 Estimated contribution of flaring activities from TIC, to SO Mass flow rates used in WRF-Chem for the three flares at MHR in Tula. Units are in 2 . SO Pollutant Scenario T0 Soot FPRPP 1 − GRO supersites. SO Table 6. Table 5. kg s Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

44 45 icate the number of the nested FPRPP (green) andFPRPP elevated(green) the flares ) ) b s s flare. The location of the cutting slices is 15220 15219 ) ) a WRF-Chem model domain. d02 and d03 indicate the number of the nested domain.

in Magenta Magenta in Figure 2. temperature Average field for sour the ga

Figure 1. a) WRF-Chem model domain. d02 and domain. d03 b) ofsupersites Location (orange), MILAGRO ind (yellow) d03. MHR in at Average temperature field for the sour gas flare. The location of the cutting slices is in 9 8 7 6 5 4 3 2 1 1 2 3 4 5 Location of MILAGRO supersites (orange), FPRPP (green) and the elevated flares (yellow) 10 11 12 13 Magenta. Fig. 2. Fig. 1. (a) at MHR in d03. (b) Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

47

46 at T0 and T1, for at T0 and T1, 2 2 mass mass rate from the combustion model d (red) time series of SO 15222 15221 Figure 3. ofComparison modeled (blue) and observe

for the simulation period.for simulation the Figure 4. Time series of EC obtained with the soot (dashed blue) and measurements (red) (dashedblue) T1 and measurements at site.

Comparison of modeled (blue) and observed (red) time series of SO Time series of EC obtained with the soot mass rate from the combustion model (dashed 1 2 3 4 3 5 6 4 1 2 Fig. 4. blue) and measurements (red) at T1 site. Fig. 3. the simulation period. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

48

49 28 28 28 27 27 27 26 26 26 ts (red)ts of EC period.for simulation the rface rface for March 23 at 12:00 LST. Left panel) panel) 25 25 25 T0 T0 T1 T2 Day Day (LST) 15224 15223 24 24 24 . 2 23 23 23 . 2 22 22 22

5 0 5 0 3 2 1 0

15 10 10 EC (ug/m3) EC

EC (ug/m3) EC (ug/m3) EC

Figure 6. Simulated plume and wind fields at the su Soot;SO Pannel Pannel Right Simulated plume and wind fields at the surface for 23 March at 12:00 LST. Left Pannel Model concentration (blue) and measurements (red) of EC for the simulation period. T0 1 2 3 4

T0 (upper panel); panel) T0 and T1 (middle T2 panel); (bottom (upper Figure (blue)5. concentration Model and measuremen Fig. 6. Soot; Right Pannel SO Fig. 5. (upper panel); T1 (middle panel) and T2 (bottom panel). 4 3 2 1 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

50 nts nts in the period from March 22 to March ee supersites. 15225

Figure 7. Suggested contribution of primary polluta 27 of 2006. Black dots show the location dots thr 27 of the location of 2006.the show Black Suggested contribution of primary pollutants in the period from 22 March to 27 March 3 4 5 1 2 of 2006. Black dots show the location of the three supersites. Fig. 7.