Nitrogen and Sulfur Emissions from the Burning of Forest Products Near Large Urban Areas

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 fuelwas consumed, 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-"

(a) (b)

(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.Differences in 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 the centerof Los NOx/CO,particulate NO•/CO and SO2/CO as well as NH3, Angeles. Nitratedeposition in thisarea is thehighest in the thebiomass was primarily Ceanothus cras$ifolius and UnitedStates, and it exceedsthat in typicalwatersheds in the Adenostomafa•ciculatum (chamise). Ceanothu• supports Pacificnorthwest by a factorof 4 or more [Rigganet al., activenitrogen fixation in root nodules, and the standing 1985]. Furthermore,while directdepositional measurements vegetationshould contain substantially more fzxed nitrogen arescarce, on thebasis of therelatively high levels of NOx and thanthe biomasses consumed in either the Eagle bum (Salvia SO2 foundin the Los Angelesbasin [Hoggan et al., 1980], mellifera,Rhus laurina (sumac and chamise)) or thePacific andthe well establisheddirect proportionality between dry Hegget al.' Nitrogenand Sulfur Emissions of Fires 1tl, 705 of SmokePlumes From the Buming of ForestProducts in SouthernCalifornia

[NO3-J, [SO4=J* [O3], [CO], [CO2], [NOx]?, [SO2], [NH3], pg m--' pg m-• ppbv ppbv ppmv ppbv ppbv ppbv

NM 3 NM 7.039.17 4.475.54 } 85 1212 375 34.126.9 •:• } 108 4644 442 >50 16 NM 59.454.0 22•:11} 106 5135 448 >100 18 NM 53 2 NM 10.719.0 4.18}4.83 185 1026 370 NM NM NM 21.424.2 11.813.2 } NM 2475 NM 41.0 13.3 200 1746 388 108 5 NM 18.7 7.55 178 1437 379 189 4 NM NM 2 NM 16.015.7 4.714.98 } 182 2330 387 353 6 NM 15.316.6 13.516.1 } 62 3298 413 21.2 20.7 17 5125 429 359 5 NM 343 6 127 NM NM 82 2730 417 166 6 NM NM NM 99 2220 397 107 BDL NM NM NM 143 1840 377 161 2 NM NM NM 141 1853 378 156 1 NM 19 BDL NM BDL 8:44•} 88 345 356 0.83 0.20 128 126 361 NM BDL -•6 NM 2 NM 5.235.85 4.263.79 } 103 422 365 7.44 4.75 111 1057 375 143 4 NM •:7031 2.993.21} 108 478 396 NM 3 NM NM 4 NM •:5144 21:8934 } 123 529 411 NM NM 71 83 359 -•6 2 NM

deposition(the dominant deposition mechanism for NOx and nitrogenemissions [Hegg and Hobbs, 1980], and it SO2) andair concentration,it is quitelikely thatdeposition of undoubtedlyproduces high deposition of thesematerials SO2 andNOx are alsoanomalously high. We postulatethat downwind.Note thatthe NOx measuredin the emissions duringburning the nitrogenand sulfur species that have been fromthis burn (250 parts per billion by volume (.ppb)) are previouslydeposited on thevegetation are volatilized, resulting comparabletothe highest measured inthe emissions from the in thesespecies being resuspended in the atmosphere. Lodibum. Although CO measurementswere not made in this Pollutant,and in particularnitrate, deposition in theregion of Pacificnorthwest burn, any reasonable assumption would the Eagleburn is probablynot as greatas in theLos Angeles yieldan NOx/CO emission ratio comparable tothose measured area,but, with the exceptionof onecase (see next paragraph), in theLodl burn and much higher than those measured in the it probablysignificantly exceeds that at therural locations in emissionsfor the otherPacific northwestbums. This the Pacific northwest for which emissions from burns are observationprovides further support for the importance of listed in Table 3. prioratmospheric deposition in determining the emissions of The interestingexception in thePacific northwest are the nitratesfrom burningbiomass. measurements obtained at the location listed under number 4 in Turningto SO2emissions, Figure 5 showsthat the SO2/CO Table 3. These measurements were obtained in the emissions ratiois alsomuch higher in theLodi burn than it is in the from a burn located ~25 km downwind of a 1000-MW coal- Pacificnorthwest. We alsoattribute this to theresuspension firedelectric power plant. Thisplant is a majorsource of odd ofpreviously deposited pollutants, since there are far more 706 Hegget al.: Nitrogenand Sulfur Emissions of Fires

TABLE 3. AverageConcentrations of VariousChemicals Across the

Location of Approximate Measurements Geographical Area Burnt, With Respectto [CI-], [NO3-•, I,ocation Fuel km2 Fire •g m-3 gg

Near Montesano, conifer slash ? mainconvective p]ume:• 6.17 19.9 ,--55 km west of (prescribedburn) mainconvective plume:• 6.27 20.9 mainconvective p.lume$ 2.90 10.2 mainconvective plume:• 3.43 10.46 mainconvective plumes 1.59 11.2 mainconvective ptume:• 1.60 11.0

---50 km southeast ---5x 106kg of 1.13 -•1.6km downwindõ NM NM of Olympia, moist conifer slash Washington. (prescribedburn ignitedby dieseloil andgasoline and hand lit)

---50 km south of conifer slash ? nearplume center{} NM NM Eugene,Oregon. (prescribedburn)

--60 km south of ---4.6x 106kg of 0.35 -•13km downwindõ NM NM Tacoma,Washington, of conifer slash and ,--25 km ENE of (prescribedburn the Centralia coal- ignitedby dieseloil and fired powerplant. gasoline)

BDL andNM indicate"below detection limit" and "not measured" respectively. Approximation sign indicates measurement could be as much as a factor of 2 in error. Parametersto theleft of the bracketsin thiscolumn were measured simultaneously be exposingtwo filters(both values are listed)while parameters tothe fight of thebrackets are average values measured over the time interval for which the filters were exposed. Ofthe NO x, 70% or more isNO 2. Measurementsaveraged over adistance of1.5 km across center ofplume. The three sets of values listed were obtained at differenttimes and locations in theplume. Measurementsaveraged over adistance of300 m across center ofplume.

sourcesof SO2in the LosAngeles basin than in thePacific northwest.And, as mentionedprev/ously, air concentrations F %o in theLos Angeles basin are in fact muchhigher than in the 300I Pacificnorthwest. Also, it is likely thatmuch of theSO2 60- o

o õ0

o z $o

20 o $ _ Olj O! I I 0 2000 4000 6000 8000 IOOOO 12000 io CO (ppbv) Fig. 3. NOx versusCO concentrationsin smokesfrom forest fh:es:the Lodi bumnear Los Angeles (circles), the Eagle bum 4000 r•X•O 8000 nearSan Diego (open triangle), and bums in thePacific CO (ppbv) northwest(squares; numbers refer to datasets as listed in Table 3). Ambientvalues have been subtracted for the Lodi Fig.4. As forFigure 3, butfor particulate NO• versusCO. andEagle measurements. The line is a bestfit to the Lodi The dashedline is a best fit to the data from the Pacific measurements.Analytical uncertainties are listed in Table 1. northwest. Hegget al.' Nitrogenand Sulfur Emissions of Fires 14,707

Centersof SmokePlumes From the Burning of ForestProducts in thePacific Northwest

[SO4=J*, [O3], [CO], [CO2], [NOx]? [SO2], },tgm-• ppbv ppbv ppbv ppbv ppbv Reference

thispaper 62'5364. } N8 11' 800 491 ,--1 -1 thispaper 24.•}26. 13 2,885 43 ,•1 ,•2 thispaper 15'38}16. ,•3 4,489 423 ,•1 BDL

NM 140 NM ,•500 20 < 2 Stith et al. [1981]; (CO2 information from J. Stith (personal communication,1986)

8.7 ,•40 7,250 367 27 BDL Radke et al. [1983]

NM ,• 100 NM NM 250 BDL Radke et al. [ 1978]

emissionsin the Pacific northwestare oxidized to sulfateeither suchfn:es for oddnitrogen may be similarto or largerthan that beforeor afterdeposition, this being the normal fate of SO2. of a coal-fn:edpower plant. However,in theLos Angeles basin, a considerableamount of Model simulationsindicate that the particles that would be S(IV) is stabilizedin organicand inorganic adducts, even in emittedinto the atmosphere by thewidespread fires that would theaqueous phase, as a resultof theabnormally high accompanya nuclear war couldcause significant decreases in concentrationsof suitablereactants, such as aldehydes globalsurface temperatures [Crutzen and Birks, 1982; Turco [Eatoughand Hanson, 1983; Richards et al., 1983];sulfur et al., 1983; National ResearchCouncil (NRC), 1985; Pittock fromsuch species will likelyvolatilize as SO2. et al., 1986]. Gaseousemissions from suchfires will also Thesimilarity in theparticulate SO•/CO ratios in the perturbthe chemistry and physics of theatmosphere. The emissionsfrom the bums in southernCalifornia and the measurementspresented in thispaper suggest that the NOx Pacificnorthwest (Figure 6) is to beexpected, since sea salt is (andpossibly, the NO• andSO•) emissionfactors that have a majorsource of sulfatedeposition in bothregions been used in numerical model simulations of the nuclear winter [Liljestrandand Morgan, 1981; Vong and Waggoner, 1983]. scenariomay havebeen too small. For example,in theNRC Indeed,estimates of sulfatedeposition derived from the andSCOPE [Pitrocket al., 1986]reports on the nuclearwinter studiesof Roberts[ 1975]and Liljestrand and Morgan [ 1981] hypothesis,the molar ratio of NOx to CO2 in smokesfrom forthe Los Angeles basin are quite similar to sulfatedeposition forestfires was taken as 3 x 10-3and 2 x 10-3,respectively. valuesderived from Vong and Waggoner [ 1983] for the Thesevalues were basedon measurementsin the laboratory Pacific northwest. [Pattersonand McMahon, 1984] andin smokesfrom forest fires in the Amazon basin[Crutzen et at., 1985], neitherof Implications which would include effects due to the remobilization of depositedpollutants from urban sources. Crutzen and Birks Whetherthe variable and unexpectedly high emissions of [ 1982]presumably used a similarratio of NOx to CO2in their nitrogenand sulfur species presented here are due primarily to originalpaper on nuclearwinter, although this is notexplicitly differencesin the compositionof the biomassor, morelikely, statedin the text. Turco et al. [1983] did not includeNOx to differentexposures to pollutants,they have implications for emissions from forest fires in their model simulations of a bothair pollution and the nuclear winter hypothesis. nuclearwinter (although they did includeNOx in the As far asair pollutionis concerned,the results presented stratospherefrom the nuclear "fireball"). hereindicate that wild firesor prescribedbums of biomass, Shownin Table4 areaverage values for themolar ratios of particularlythose near major urban areas, may be major NOx to CO2 andNOx to CO derivedfrom the measurements sourcesof oddnitrogen and S(IV). Thesource strengths of presentedhere and from values that have been measured or 14,708 Hegget al.: Nitrogenand Sulfur Emissions of Fires

70-

[31 2øI o 60

< 20

155 •o I0

0 •:• ;9 I I I I I /o oo• 0 2000 4000 6000 8000 I0000 12000 CO (ppbv) ø1 I I I I I o• :•ooo40o0 60o0 8000 I0000 12000 Fig.6. Asfor Figure 3, butfor particulate SO• versusCO. CO (ppbv) The line is a bestfit to boththe southernCalifornia and Pacific Fig.5. Asfor Figure 3, butfor SO2 versus CO. northwest data.

TABLE4. Averagesand Standard Deviations forthe Ratio of NO x toCO and NO x toCO7, in Smokes Fires Locationof Fire NOx/CO NOx/CO2 Comments

i i NearLos Angeles 0.08+ 0.03 0.006+ 0.003 measurementspresented in thispaper (Lodi Burn) (If theNOx/CO 2 ratiois calculatedfrom our measuredNOx/CO ratio using Pittock et al.'s

[1986]value forß CO/CO2(=0.13), a valueof 0.011 is obtmnedfor NOx/CO2 . Our measurementsgive a ratioof CO/CO2of 0.072 + 0.018.) NearSan Diego 0.14 0.013 measurementspresented in thispaper (EagleBurn) Near Montesano, <10-4 <10-5 measurementspresented in thispaper -•55 km westof Olympia, Washington -•50 km southeast of 0.0001 Radke et al. [1983]. Olympia,Washington --50 km south of 0.003 0.0001 Radke et al. [ 1983] Eugene,Oregon

Several different locations 0.02-0.1 0.003- 0.017 NOx/CO2ratio is calculatedfrom in the United States Sandberget al.'s[1979]measurements of NOx/CO,using Pittock et al.'s[1986] CO/CO2 ratio. Nuclearwinter numerical 0 -0.023 0-0.003 TheNOx/CO 2 valuescover the range model simulations usedby Crutzenand Birks [1983], Turco et al. [1983],National Research Council [1985],Thompson and Schneider [1986], Vupputuri[ 1986], and Pittock et al. [ 1986]. TheNOx/CO values were calculated from theNOx/CO 2 values using Pittock et al.'s [ 1986]value for CO/CO2.

Ambientconcentrations of the gases have been subtracted. * Thismethod isoften used to determine NOx/CO2. We measured both NOx/CO and NOx/CO2; the former is more accuratebecause ofthe large contrast between CO concentrations insmoke and ambient aircompared toCO2. Hegg et al.: Nitrogenand SulfurEmissions of Fires 1•4,709 usedby otherworkers. The ratiosNOx/CO2 and,in Hoggan,M., A. Davidson,and D. Shikiya,Seasonal and particular,NOx/CO that we measuredin theLodi and the Eagle diurnalvariation in air qualityin California'ssouth coast burnsare more than an orderof magnitudelarger than the air basin,Report from SouthCoast Air Quality values for these ratios that we have measured in more rural ManagementDistrict, E1Monte, California, 1980. locations,and 2-4 timeslarger than the largest values that have Liljestrand,H. M., andJ. J. Morgan,Spatial variations of been used in numerical model simulations of the nuclear winter acidprecipitation in southernCalifornia, Environ. Sci. scenario.In thecompilation of emissionratios by Sandberget Teqhn01., 15, 333-338, 1981. al. [ 1979], valuescomparable to thosewe measuredin the NationalResearch Council, The Effectson theAtmosphere 0f Lodi andEagle burnscan be found,although most of their a Maior NuclearExchange, National Academy Press, values are lower than ours. Wasfiington,D.C., 1985. What weightshould be givenin numericalmodeling studies Patterson,E. M., andC. K. McMahon. Absorption of the nuclearwinter hypothesisto the high valuesof NOx/CO characteristicsof forestfire particulatematter, Atmos. that we have measured in smokes from fires near urban areas Environ., 18, 2541-2551, 1984. in southernCalifornia? Certainly,this region cannot be Pitrock, A. B., T. P. Ackerman, P. J. Crutzen, M. C. consideredas representativeof forestedareas in general. MacCracken,C. S. Shapiro,and R. P. Turco, However,for reasonsoutlined in the followingparagraph, the EnvironmentalConsequences of NuclearWar, V01. 1. NOx/CO valueswe measuredin southernCalifornia may be Physicaland A•;mospheric Effects, J. Wiley, New York, morerepresentative for numericalmodeling studies of nuclear 1986. winter than those for rural areas. Radke,L. F., J. L. Stith, D. A. Hegg, and P. V. Hobbs, First,pollutant deposition is commonplacenear large urban Airbornestudies of particlesand gases from forestfires, J. areas. Indeed,nitrogen deposition in westernEuropean Air P011Ut,!•ontrol Assoc., 28, 30-34, 1978. woodlandscan be asmuch as 3 timesgreater than that in the Radke, L. F., J. H. Lyons, D. A. Hegg, and P. V. Hobbs, Los Angelesbasin [van Breemanet al., 1982]. Second,in a Airbornemonitoring and smoke characterization of nuclearwar, urbanareas could be preferentialtargets. Finally, prescribedfires on forestlands in westernWashington and it is importantto note that we do not know what fractionof the Oregon,EPA Rqport600x-83-047, Environmental remobilizedpollution is derivedfrom the burningof the forest MonitoringSystems Laboratory, Office of Researchand productsthemselves (i.e., plantmaterials) and what fractionis Development,U.S. Environ.Prot. Agency, Las Vegas, derivedfrom the heatingand burning of the forestfloor. If a 1983. significantfraction originated from surfacematerials and soils, Richards,L. W., J. A. Anderson,D. L. Blumenthal,J. A. thenremobilized pollution will probablyincrease the emission McDonald,G. L. Kok, andA. L. Lazrus,Hydrogen factorsfrom the burningof othermaterials subject to peroxideand sulfur (IV) in Los Angelescloud water, depositionand accumulationof urbanpollutants. This overall A•mo•. Environ,, 17, 911-914, 1983. increasein NOx emissionsfrom combustionof ground Riggan, P. J., R. W. Lockwood,and E. N. Lopez, materialcould render such NOx emissioncomparable, or Depositionand processing of airbornenitrogen pollutants possiblyeven greater than, those produced in nuclearfireballs. in Mediterranean-typeecosystems of southernCalifornia, In view of theseconsiderations, we suggestthat the NOx Environ. Sci, Te•hnol..,,19, 781-789, 1985. emission factors that we have measured in southern California Roberts,P., Gas-to-particleconversion: Sulfur dioxide in a may be morerepresentative than tho•e that havebeen used to photochemicallyreactive system, Ph.D. Thesis, California datein numericalmodeling studies of the nuclearwinter Instituteof Technology,1975. (Availablefrom Xerox scenario. UniversityMicrofilms, Ann Arbor,Mich). Sandberg,D. V., J. M. Pierovich,D. G. Fox, and E. W. Acknowledgments.Thanks are aue to all of those,too Moss, Effectsof Fire on Air, Gen. Tech. Rep. WO-9., numerousto mentionby name,who participated in theLodi U.S. Dept. of Agric., ForestServ., 1979. Canyonfire experiment.Support and management of fire Stith, J. L., L. F. Radke, and P. V. Hobbs, Particle emissions operationsfor theLodi burnby theAngeles National Forest, andthe production of ozoneand nitrogen oxides from the Countyof LosAngeles Fh'e Department and the California burningof forestslash, Atmos, Environ., 15, 73-82, Departmentof Forestryare gratefully acknowledged. This 1981. researchwas supportedby the DefenseNuclear Agency, Thompson,S., andS. Schneider,Nuclear winter reappraised, throughfunds made available under NRL contractN00014- Foreign Aft., 64, 981-1005, 1986. 86-C-2246. Turco, R. P., O. B. Toon, T. Ackerman, J. B. Pollack, and References C. Sagan,Nuclear winter: Global consequences of multiplenuclear explosions, Science, 222, 1283-1293, Crutzen,P. J., and J. W. Birks, The atmosphereafter a 1983. nuclearwar: Twilight at noon,Ambi0,, 11, 114-125, van Breeman,N., P. A. Burrough,E. J. Velthorst, H. F. van 1982. Dobben,T. de Witt,T. B. Ridder, and H. F. Reijnders, Crutzen,P. J., A. C. Delany, J. Greenberg,P. Haagenson, Soil acidificationfrom atmosphericammonium sulfate in L. Heidt, R. Lueb, W. Pollack, W. Seiler, A. Wartburg, forestcanopy throughfall, Nature, 299, 548-550, 1982. andP. Zimmerman,Tropospheric chemical composition Vong, R., and A. Waggoner,Measurements of the Chemical measurementsin Brazil duringthe dry season,J. Atmos. Compositionof WesternWashington Rainwater, 1982- Chem., 2, 233-256, 1985. 1983, Reportto Environ.Prot. Agencyregion 10, Univ. Eatough,D. J., andL. D. Hanson,Organic and inorganic of Wash., Seattle, 1983. S(IV) compoundsin airborneparticulate matter, Adv. Environ. Sci. Technol., 12, 221-225, 1983. C. A. Brock, D. A. Hegg, P. V. Hobbs,and L. F. Radke, Evans,L. F., N. K. King, D. R. Packham,and E. T. Cloudand Aerosol Research Group, Department of Stephens,Ozone measurements in smoke from forest AtmosphericSciences, University of Washington,Seattle, fires, Environ, Sci. Technol., 8, 75-81, 1974. WA 98195. Evans, L. F., F. A. Weeks, A. J. Eccleston, and D. R. P. J. Riggan,U.S. ForestService, 4955 CanyonCrest Packham,Photochemical ozone in smokefrom prescribed Dr., Riverside, CA 92507. burningof forests,Environ, Sci, Technol.,11,896-900, 1977. Hegg, D. A., andP. V. Hobbs,Measurements of gas-to- (ReceivedJune 10, 1987; particleconversion in theplumes from five coal-fired revisedSeptember 1, 1987; electricpower plants, Atmos. Environ,, 14, 99-116, 1980. acceptedOctober 12, 1987.)