JOURNALOF GEOPHYSICAL RESEARCH, VOL. 92, NO. D12, PAGES14,701-14,709, DECEMBER 20, 1987 NITROGEN AND SULFUR EMISSIONS FROM THE BURNING OF FOREST PRODUCTS NEAR LARGE URBAN AREAS Dean A. Hegg, LawrenceF. Radke,Peter V. Hobbs,and CharlesA. Brock Cloudand Aerosol Research Group, Department of AtmosphericSciences Universityof Washington,Seattle Philip J. Riggan U.S. Forest Service, Riverside, California Abstract.Airborne measurements of tracegases and horizontallyat 2000-2400m abovemean sea level (MSL), particlesin the smokefrom a prescribedbum of forest with somehotter columns penetrating above 'these levels. productsin the LosAngeles basin show significantly higher We will alsopresent some airborne measurements obtained emissionsof NOx, SO2,and particulate NO• thando in the smokefrom a prescribedbum ignitedon December3, measurementsin smokesfrom theburning of biomassin rural 1986 near Ramona, California (33ø3'30"N, 116ø55'30"W). areas.It is postulatedthat the high emissions are due to the This bum involveda 30-hectare(0.3 km2) subunitin which revolatilizationof previouslydeposited pollutants. 2 kg m-2of fuel wasconsumed, consisting of coastalsage Implicationsfor pollutantsource inventories and the nuclear scrubdominated by blacksage (Salvia mellifera), sumac winterhypothesis are briefly discussed. (Rhuslaurina), and chamise (Figure 2). We will call thisthe Eaglebum. Introduction AirborneInstrumentation and Sampling Studiesof the emissionsof particlesand gases from forest Procedures firesand prescribed burns of forestproducts were initially cardedout to determinetheir effects on air quality[e.g., Radke The measurementsto be describedhere were obtained et al., 1978, 1983; Sandberget al., 1979]. Recently,interest ab6'ardthe University of Washington'sConvair C-. 131A in suchstudies has broadened to includethe effects of burning researchaircraft (Table 1). Smokesamples were obtained by on globalchemistry [e.g., Crutzenet al., 1985] and on the allowingram-air pressure tofill a polyethylenebag, 1.5 m-3 in environmentalconsequences of nuclearwar, the so-called volume,aboard the aircraft. The variousmeasurements listed "nuclearwinter hypothesis" [Crutzen and Birks, 1982;Turco in Table1 wereobtained by drawingsamples from this bag. et al., 1983]. Thebag was filled in 16s whenthe aircraft was located near This paperis concernedwith a preliminarydescription of thecenter of themain convective plume from the fire. (The airborne measurements obtained in the emissions from a centerof theplume was considered to belocated where the prescribedbum of forestproducts that took place near Los particlenumber concentration and light-scattering coefficient Angeleson December12, 1986. Comparisonof these reachedpeak values. Both of theseparameters were measured measurements with those obtained from bums in more rural continuouslyaboard the aircraft.) areasreveals significant differences in nitrogenand sulfur emissions. Results Descriptionof the Burns Chemical measurements obtained in the smokes from the Lodi andEagle bums are listed in Table2. For comparison, Theprescribed burn near Los Angeles, California, was we list similar measurementsin Table 3, obtainedin the Pacific designedto characterize gaseous and particulate emissions northwest. The concentrationsof NOx and SO2 in the froma relativelylarge chaparral fire andto relatethe emissions emissionsfrom the Lodi bum, and to a lesserextent the NOx to remotelysensed fire radiativeemissions, heating, and fromthe Eagle bum, are much higher than those measured in smokeoptical properties. Located in LodiCanyon (34ø10'N, the smokes from the burns in the much more runfi areas of the 117ø47'W),on the SanDimas Experimental Forest, the Pacificnorthwest. Also, the NH3 measuredin theplume from prescribedbum encompassed ~40 hectares (0.4 km2) of the Lodi bum is unusuallyhigh. chaparralthat was last burned by wildfirein 1960. The bum The dichotomybetween the measurements in southern consumed3-6 kg m-2of foliage,deadwood, and small- Californiaand the Pacificnorthwest is clearlyshown in diameterlive stemsof Ceanothuscrassifolius and Adenostoma Figures3-5; theratios NOx/CO, particulate NO•/CO, and fasciculatum(chamise). Hereafter, we will refer to thisas the SO2/COin the smokefrom the Lodi burn(and NOx/CO in the Lodi burn. smokefrom the Eagle bum) were all muchgreater than they The Lodi bum occurredon December12, 1986 (Figure 1). were in the smokes from the bums in the Pacific northwest. It wasignited by flaminggasoline-gel globules dispensed from However,this dichotomy does not appearin theratio a helicopter.(We notethat this fuel contains only insignificant particulateSO•/CO (Figure6). levelsof eithersulfur or nitrogen.)Flames were commonly 6- Near themiddie and upper part of theplume of smokefrom 12 m in length,with low ratesof forwardspread. Soil surface theLodi bum, the ozoneconcentrations were higher than in temperaturesduring burning peaked at about850øC (F. the ambientair, while near the baseof the l•lume, the ozone Weirich,personal communication, 1986). Thebum produced concentrationswere lower than ambient. Ozone deficits in the a seriesof discreetplumes, which tended to spreadout smokesfrom fires are to be expectedand have been observed previously[e.g., Stith et al., 1981];they are due to both Copyright1987 by theAmerican Geophysical Union. heterogeneousand homogeneous reactions of ambientozone withplume constituents. Ozone production in fireplumes has Papernumber 7DO799. alsobeen observed previously [Evans et al., 1974;Radke et 0148-0227/87/007D-0799505.00 al., 1978;Stith et al., 1981];it maybe dueto photochemical 14,701 14,702 Hegg et al.' Nitrogenand SulfurEmissions of Fires ., ....... ,...• ?•.,•,•..:.,•;.•.•.•.•..,.... •.::.... 'i'i-" ß (a) (b) (c) (d) (e) Fig.1. Viewsofthe Lodi burn at (a) 1106 PST (1 hour9 min after ignition), (b)1154 PST, (c) 1210 PST, (d)1228 PST, and (e) 1322 PST on December 12,1986. (Photographer: PeterV. Hobbs) Hegget al.: Nitrogenand Sulfur Emissions of Fires 1•4,703 Fig. 2. View of the Eaglebum at 1200PST on December3, 1986. TABLE 1. Measurements Obtained Aboard the C-131A Aircraft That are Utilized in the Present Analysis Parameter Instrumentor Technique AnalyticalUncertainty Soluble filtration with 47-mm SO• + 4% or better;NO• + 11% particulate stretched Teflon filter or better; C1- + 14% or better anions (Gelman) 03 MonitorLabs 8410 +5 ppb (C2H4 chemiluminescent) NO2, NO MonitorLabs 8840' +1 ppb (03 chemiluminescen0 SO2 TecoSP 43* +1ppb (pulsedfluorescence) CO Teco 48 + 100 ppb (correlationIR spectrometer) CO2 Miran 1A +4 ppm (IR spectrometer) NH3 filtration with oxalic acid- +15% or better impregnatedfilter preceded by Teflon filter *Modifiedin house. 1•4,70J4 Hegget al.: Nitrogen and Sulfur Emissions ofFires TABLE 2. AverageConcentrations of VariousChemicals Across the Centers Location of Approximate Measurements Geographical Area Bumt, With Respectto [C1-], Location Fuel km2 Fire •tgm-3 San Dimas standingchaparral 0.4 mainconvective p]ume•: BDL ExperimentalForest, andbrash (prescribed mainconvective plume•: 1.23 located about 10 km burnignited with jellied mainconvective p!ume•: 9.01 north of Pomana, near gasolineby helicopter) mainconvective plume•: BDL Los Angeles,Califomia. mainconvective plume•: 9.70 ("Lodi" burn). mainconvective plume+, 7.75 6.5 km downwind BDL 6.5 km downwind BDL mainconvective plumes 2.3 mainconvective plume$ 3.10 -•8 km downwind 1.84 -•9.5 km downwind BDL -• 10.5 km downwind BDL -•10.5 km downwind BDL e•ge of themain convective plume 5.81 ge of the main convectivep•ume 7.19 mainconvective plume•: 6.11 mainconvective plume•: BDL mainconvective plume•: NM mainconvective plume•: NM -• 10.5 km downwind NM -• 10.5 km downwind NM ambient air above the BDL surfaceinversion layer BDL same as above BDL mainconvective plume•: 1.08 mainconvective plume• 1.29 About 2.5 km east of coastalsage scrub 0.3 mainconvective plume•: BDL Ramona and -•40 km NE mainconvective plume•: BDL of SanDiego, California mainconvective plume+,. BDL ("Eagle"bum). mainconvective p.lume•: BDL mainconvective p•ume•. BDL ambient air above the NM surfaceinversion layer BDLand NM indicate"below detection limit" and "no measurement", respectively. Approximation sign indicates that measurementscould be as much as a factor of 2 in error. Parameterstothe left of thebrackets in thiscolumn were measured simultaneously byexposing two filters (both values listed)while parameters tothe fight of thebrackets are average values measured over the time interval for which the twofilters were exposed. Ofthe NO x, 70% or more isNO 2. Measurementsaveraged overa distance of-•l.5 km across center ofplume. reactionsnear the topof a plumeas it mixeswith the ambient northwestburns (primarily P. menzi•,•ii(Douglas fir)). air [Evans et al., 1977]. However,this would leave unexplained both the highNOx/CO ratioin theEagle bum andthe high SO2/CO ratio in theLodi Discussion burncompared to thosein the Pacificnorthwest bums. An alternative,and we believemore likely, explanationfor Severalpossible explanations can be suggested for the the differences in the emissions between the bums in southern differencesin the emissionsfrom the bums in southern Califomia and Pacific northwest lies in differences in the California and the Pacific northwest. Differencesin the depositionof pollutantsto thev•getafion. Lodi Canyonis compositionof the biomass undergoing combustion might be locatedjust 10 km northof the SanBemadino Freeway responsible.In theLodi burn, which produced high ratios of (Interstate10) and -•50 km to the eastof