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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 99, NO. DI, PAGES 1805-1819, JANUARY 20, 1994

Acetone in the atmosphere:Distribution, sources,and sinks

H. B. Singh,• D. O'Hara,2 D. Herlth,• W. Sachse,s D. R. Blake,4 J. D. Bradshaw,5 M. Kanakidou,• and P. J. Crutzen7

Acetone(CH3COCH 3) was foundto be the dominant nonmethaneorganic species present in the atmospheresampled primarily over easternCanada (0-6 kin, 35ø-65øN)during ABLE3B (July to August 1990).A concentrationrangeof 357to 2310ppt (=10 -12 v/v) with a meanvalue of 1140+ 413ppt was measured.Under extremelyclean conditions,generally involving Arctic flows, lowest (background) mixing ratios of 550 _+100 ppt were presentin much of the tropospherestudied. Correlationsbetween atmosphericmixing ratiosof acetoneand selectspecies such as C2H2, CO, C3H8, C2C14 and provided important clues to its possible sources and to the causes of its atmospheric variability. Biomassburning as a sourceof acetonehas been identified for the first time. By using atmospheric dataand three-dimensional photochemical models, a global acetone source of 40-60Tg (=1012 g)/yr is estimated to be present. Secondary formation from the atmospheric oxidation of precursor hydrocarbons(principally propane,isobutane, and isobutene)provides the single largest source (51%). The remainderis attributableto biomassburning (26%), direct biogenicemissions (21%), and primary anthropogenicemissions (3%). Atmosphericremoval of acetoneis estimatedto be due to photolysis (64%), reaction with OH radicals(24%), and deposition(12%). Model calculationsalso suggestthat acetonephotolysis contributed significantly to PAN formation(100-200 ppt) in .the middle and upper troposphereof the sampledregion and may be important globally. While the source-sink equation appearsto be roughly balanced,much more atmosphericand sourcedata, especially from the southern hemisphere,are neededto reliably quantify the atmosphericbudget of acetone.

INTRODUCTION While several carbonyl species have been studied in polluted atmospheres[Vairavamurthy et al., 1992], formalde- Natural and anthropogenic nonmethane hydrocarbons hyde is the only one to receive significant attention in (NMHCs) are released into the atmosphereat a rate of nearly global tropospheric chemistry studies. One of the most 103Tg/yr [Duce et al., 1983;Singh and Zimmerman, 1992]. abundant reactive oxygenated species in the remote Atmosphericreactions of these NMHCs with ozone (03) and atmosphereis acetone.It was first measuredby Cavanagh et free radicals result in the formation of a variety of a l. [1969] at a of about 1 ppb in the intermediate oxygenated species of which carbonyls uncontaminated Arctic air of Point Barrow, Alaska. Singh (RR'C=O) form an important group [National Academy of and Hanst [1981] used a photochemical model to suggest Sciences (NAS, 1976; Lloyd, 1979; Atkinson, 1990]. There that acetone is an ubiquitous atmospheric species resulting is further evidence that direct emissionsof carbonyl species from the oxidation of propane. They also showed that from both natural and manmade sourcesare also quite com- acetone can produce free radicals which sequester reactive mon [NAS, 1976; Isidorov et al., 1985; Sigsby et al., 1987]. in the form of PAN. Recent photochemicalstudies Carbonyl compoundsare of interest to atmosphericchemists have used one-dimensional and two-dimensional models to because of their potential toxicity, their ability to photolyze describe its atmospheric structure based on its source and produce free radicals, their ability to form stable atmo- resulting from the oxidation of such as propane spheric products, and their interactions in the cycles. and isobutane [Kasting and Singh, 1986; Chatfield et al., Because they are frequently intermediate products of atmo- 1987; Singh and Kasting, 1988; Henderson et al., 1989; spheric oxidation, these molecules can serve as excellent Kanakidou et al., 1991]. Data to support these model results tracers for the validation of photochemicalmodels. unfortunately are extremely sparse,in part becauseof lack of suitable measurement techniques [Vairavamurthy et al., 1992]. Table 1 summarizes available measurements of •NASA AmesResearch Center, Moffett Field, . acetone,most of which were made at rural surfacesites using 2SanJose State University Foundation, Moffett Field, California. a variety of direct and indirect techniques. The only SNASALangley Research Center, Hampton, . measurementsthat are not made on the ground are those of 4Universityof California,Irvine. SGeorgiaInstitute of Technology,Atlanta. Arnold et al. [1986] who used an indirect chemical ionization SCentredes Faibles Radioactivit•s, Laboratoire mixte CNR$/CEA, Gif- technique, applicable in the upper troposphereand the lower sur-Yvette, France. , to estimate acetone abundances. The wet ?MaxPlanck Institute for Chemistry,Mainz, Germany. chemical derivative techniques such as the DNPH/HPLC method have also been used for and ketones in Copyfight1993 by the AmericanGeophysical Union. semipolluted environments, but these require long sampling number 93JD00764. times and suffer from potential interferences[Vairavamurthy 0148-0227/93/93JD-00764505.00 et al., 1992]. Overall, few reliable measurements of acetone

1805 1806 SINGH ET AL.' ACETONE IN THE ATMOSPHERE

TABLE 1. AcetoneConcentrations in the Rural/RemoteAtmospheres

Acetone Mixing Ratio, ppb N Method Location Source 1.0 .(ND-2.9) 25 Surface 'grabsample ' PointBarrow' Alaska, Cavanaghet al. GC/FID 71 øN [19691 1-3 - surface grab sample westernUnited States Robinson et al. GC/FID [1973] 0,47+0.09 5 surface grab sample Atlantic air, Penkett GC/MS 35øN [1982] 2.8+0.8 18 surface condensate rural sites in Arizona Snider and Dawson GC/FID [1985] 0.1-0.2 19 upper troposphere, CIMS, over Europe, 45øN ArnoM et al. 6-10 km indirect method [1986] 1.7+0.8 96 surface DNPI-I/HPLC, rural sites in Shepsonet al. wet chemical southern Canada, 45øN [1991] 1.14_+0.41 , 123 free troposphere, cryosample North America, this study 0-6 km GC-RGD 35-65øN ND,not detectable; N, number of datapointsl CIMS, chemical ionizatioh mass spectrometery; DNPH, Dinitrophenyl hydrazine;HPLC, high performanceliquid chromatography;RGD, reductiongas detector. are available in the global troposphereand very little about key species with capillary column, and sensitivedetec- its sources and sinks is known. tion by a mercuric reduction gas detector (RGD). The During the summer (July to August) of 1990, NASA RGD is based on the UV detection of vapor released GTE/Arctic BoundaryLayer Expedition(ABLE)3B experiment when a speciesX reacts with heated (285øC) mercuric oxide provided an opportunity to utilize a recently developed (X+HgO() --> XO+Hg(vapor)). It has been previously instrument to perform real-time airborne measurementsof shown by O'Hara and Singh [1988] that RGD can detect acetone between 35øN and 65øN to an altitude of 6 km. In acetone and (and possibly ) with a addition, a comprehensiveset of trace chemical (03, NOx, sensitivity that is 20 to 30 times greater than that of FID. NOy, PAN, HNO3, C2-C6 NMHC, CO, )and Since the RGD is also sensitive to other species such as meteorological parameters were also measured. Here we , compounds, and some higher hydrocarbons, present the first airborne measurementsof acetone based on the analytical technique devised used a precolumn (with time- its direct real-time detection and use these to characterize its programmed backflush) to reduce potential chromatographic distributions and variabilities in the troposphere. interferences. Relationships between the atmospheric of Species of interest, such as acetone, were cryogenically acetone and other key chemical parameters are explored. (-170øC) enrichedfrom a 300 ml (0øC, 1 atm) air samplein a Based on the interpretation of these field measurementsand multistage open tube trap connectedto a ten-port gas sample the exercise of photochemicalmodels, we construct a rough valve. The concentrate was then injected into a precolumn picture of its sources and sinks. containing two stationary phases. The first section of the packed precolumn was 20 cm x 0.18 cm ID section of 10% EXPERIMENT carbowax 600 on Supelcoport connectedto a second section of 30-cm length containing 0.2% carbowax 1500 on ABLE3B utilized a Lockheed Electra for all aircraft Carbopack. The precolumnsand valve assemblywere held at measurements.Instrument integration and flight tests were 42øC. The compoundsflushed through the precolumn were performed at Wallops Island, Virginia. Aircraft missionswere cryofocusedin second dual stage trap attached to a six-port conducted from July 5 to August 15, 1990, primarily from valve. When acetone was collected in the secondtrap (time North Bay (46.3øN, 79.5øW) and Goose Bay (53.3øN, program), the two precolumn was backflushed to 60.4øW), Canada. Field missions were divided into generic substantially eliminate potential interferences such as types that included boundary layer flux measurements, and high boiling organics. Trapped material from the second midtroposphericdistributions, and vertical profiles. A lati- precolumn was injected into the main analytical column by tude of 35ø-65øN over 60ø-80øW longitude was covered during heating it to 70øC. The main analytical column itself was a this experiment. Transit flights provided limited opportuni- 30 m x 0.75 mm 1/•m Supelcowax 10 glass capillary ties to study the latitudinal distribution of species. column fitted with a 0.2 m x 1 mm 10% carbowax 1000 on Geographical extent covered during the ABLE3B missions Supelcoportguard column. A helium carrier gas flow rate of and a summary table of individual flights are provided in the 10cm3/min and an isothermal oven temperature of 47øC were overview paper by Harriss et al. [this issue]. employed.A makeup flowof 10 cm3/minwas provided to The PANAK instrument was designed to measure allow the RGD to receivea total of 20 cm3/minof helium. peroxyacetylnitrate (PAN) and select and ketones In-flight calibrations were performed with the help of an using a pair of airborne gas chromatographs.Results based acetone permeationtube (VICI-Metronics) held at 0øC in an on the measurementsof PAN and other reactive nitrogen icepoint flight dewar. This tube permeated at a mean rate of speciesare discussedin a companionpaper [Singh et al., this 58 ng/min of acetone. A dynamic dilution system using issue]. The initial focus for carbonyl measurementswas on compressed ultrazero air was used to generate acetone acetone and acetaldehyde.The instrument used dependedon standards in the 50 to 3000 ppt range bracketing actual cryogenic collection of about 300 ml of air, separation of tropospheric measurements. To ensure that the permeation SINGH ET AL.: ACETONE IN THE ATMOSPHERE 1807

6 2500

45 ø - 65 ø N 2000

Acetone 1500

• 3 1000

500 Ethane

o 0 10 20 30 40 50 60 70 80 90 100

0 200 400 600 800 1000 1200 Percent

Acetone (ppt) Fig. 2. Frequencydistribution of acetoneand ethane mixing ratios. Ethane data correspond to those missions for which acetone Fig. 1. Linearity of acetonecalibration over a typical concentration measurements were also available (missions 13-22). Unless range using the gas chromatographic-reductiongas detector (GC- RGD) system. otherwisestated, all data presentedin this and subsequentfigures represent measurements over 45ø-65øN latitude and 60ø-80øW longitude. tube was uncontaminatedand behaved properly, laboratory standardswere prepared in a variety of medium and meteorological patterns responsible for the of compared with the acetone standards generated from the acetone and other trace species from a variety of source acetone permeation tube. These comparisons agreed to regions. Since acetonehas significant secondarysources and typically within 10% and confirmedthe purity of the acetone a relatively short lifetime, differencesin chemicalproduction emission. It is noted that the same studies also showed that and destructionrates can also cause atmosphericgradients the acetaldehydepermeation tube did not work properly and and variability. As is discussed later in this paper, the gravimetric loss rates did not correspondto acetaldehyde atmosphericlifetime of acetoneis longer than 10 days and emissionsover a period of several weeks. One of the causes was found to be the slow oxidation of acetaldehydeto . In the field, all calibrations were performed with the ß I ' ! ' I ' ! " (a) acetone permeation system. As is shown in Figure 1, the 45.65øN detector is linear in the concentration range of interest. ABLE3B provided the first opportunityfor the deploymentof this GC-RGD system aboard an aircraft. During field operation the system had a sensitivity of 10 ppt acetone (300-m! standardsample) and a measurementwas made about every 12 min. The sampling frequency was in part dictated by the fact that the RGD system sharedits computercontrol with the PAN instrument. A precision of +10% and an overall accuracyof about +15% are estimated. ß I ß ; , I , , I

RESULTS AND DISCUSSION 400 800 1200 1600 2000 Acetone (ppt) Acetone measurementswere made starting with the Goose Bay operation and continued till the end of ABLE3B ! (b) (missions13-22). An integrateddata file, containingacetone 45-65øN data and the correspondingmixing ratios of a large variety of trace species measured by ABLE3B investigators, was created for the purpose of data analysis. These complemen- tary data were averagedwithin the acetonesampling window. In the analysis and interpretation that follows, it is importantto rememberthat all measurementsare not exactly overlappingin time and space.

AtmosphericDistribution of Acetone 0 I I I Acetone was found to be an ubiquitous componentof the 400 700 1000 1300 1600 atmosphere and was measured in a concentration range of 357 to 2310 ppt. Substantial variability in the atmospheric Ethane (ppt) abundance of acetone was observed and its vertical structure Fig. 3. Mean vertical structure of (a) acetone and (b) ethane. varied from day to day. This variability was associatedwith Horizontal bars show one standard deviation. 1808 SINGH ET AL.' ACETONE IN THE ATMOSPHERE long-range transport is clearly possible. The mean acetone concentration observed during this entire effort was 1140 + 413 ppt (n=123). Figure 2 shows the frequency distribution of acetone and ethane based on data collected during ABLE3B. Ethane is thought to be the most abundant non- organic species in the global atmosphere [Singh and Zimmerman, 1992]. It is clear from Figure 2, that ace- tone was more abundant than ethane during this entire experiment. The possibility clearly exists that oxygenated species (such as carbonyls, alcohols, ethers) are important components of the global atmospherebut have not yet been fully investigated. Figure 3 shows the vertical structureof acetone and ethane as measured in the 45ø-65øN latitude belt. The mean acetone vertical profile is nearly constant with substantialvariability at all levels. Frequently mixing ratios were higher aloft than near the ground. The lowest mixing ratios were found during clean Arctic air episodesand coincidedwith low CO, NMHC, C2C14,and 0 3 values.Table 2 showsdata involving two such periods encountered in the free troposphere (4-6 km, mission 14) and the boundary layer (0-2 km, mission 18). Trajectory analysis performed by Shiphamet al. [this issue] indicate that the air masses encountered during mission 14 probably originated in the subtropical Pacific some 15 days earlier and were influenced by the Arctic/subarcticair en route to the sampling area. The lowest mixing ratios observedin the free tropospherewere in the 500-to 600-ppt range, while the lowest levels encountered in the surface air were in the 350-to 400-ppt range. The latter were found in clean Arctic air masses and over water bodies (e.g., missions 18 and 19 over Frobisher Bay). As will be discussedlater in this paper, it is possible that important amounts of acetone are exchanged(but probably not lost) acrosswater bodies. Table 2 also shows the extremely low levels of other primary and secondarytracers present in these air masses.For example, the PAN concentrations measured in this 4-to 6-km altitude were among the lowest ever encountered. It is evident that backgroundmixing ratios of at least 400 to 600 ppt could be found in much of the troposphere studied during ABLE3B o (0-6 km). The surface mean of 1140 ppt and clean background mixing ratios of =500 ppt are in general agreement with the limited surface data from the Arctic reported by Cavanagh et al. [1969] and over the Atlantic reported by Penkett [1982]. The results in this study, however, show significantly higher acetone abundancesat 6 km than those indirectly estimated by Arnold et al. [1988] from a technique based on chemical ionization mass spectrometry (CIMS). The reasons for these differences are not clear. Missions 18-22 provided an opportunity to study the latitudinal behavior of acetone and other trace chemicals over a latitudinal belt of 35ø-63øN (60ø-80øW longitude) during early August. These limited data cannot be considered to provide a robust latitudinal profile given the observedvari- ability in the atmosphericabundance of acetone.However, a general behavior similar to that of CO (and C2H2) is indi- cated. Figure 4 uses data from four select missionsto show the vertical structure of acetone and CO at four latitudes. A significant change in the boundary layer concentrationsis evident. This is direct evidence for substantial surface emis- sions of acetone and its precursors at lower latitudes. This general feature is also seen in the corresponding vertical profiles of tracers with significant anthropogenic sources SINGH ET AL.' ACETONE IN THE ATMOSPHERE 1809

I I I shipspoint to the commonsources of CO, C2H2 andC3H8, (a) and acetone. The relationshipwith C2C14 is weaker in part because of the difficulty in resolving small changes in its measured concentrations of less than 20 ppt (precision=2 5 ppt) above a background of about 10 ppt. This background itself is somewhat variable because of hemispherical scale gradientsin the mixing ratio of C2C14 due to its moderately short lifetime (--6 months). Other tracers such as CFCs showed worse precision problems and were not used. Indeed, ß I ß'. © '\ '\ 37ON air masseswere strongly influenced by biomassburning in this region [Shipham et al., this issue]. Figure 7 shows the 57øN ß samerelationships with oxidizedspecies such as NOy, PAN, 52ONIZI 45ON and 0 3. Although these data are much more scattered,they still suggestthat the sourcesthat impact the distribution of 625 1250 1875 2500 acetonealso have a substantialimpact on NOy,03, andPAN. Acetone (ppt) These relationships in the context of ABLE3B support biomass burning and industrial as two important I I (b) sources of acetone which are also responsible for much of the observed atmosphericvariability. M O19 5 ID 20 CaseStudies of BiomassBurning and IndustrialPollution •21 O 22 Biomass burning as a source of acetone. Air masses strongly affected by forest fire plumes were sampledduring ABLE3B. In virtually all cases an enhancementof acetone was observed. Figures 8 and 9 present examples of cases where the sampled air was impacted by forest fire plumes. During mission 13 a forest fire plume was sampledbetween 1

(• and 3 km (Figure 8). The unaffectedC2C14 (as well as several anthropogenic halocarbons) rule out the 0 100 150 200 possibility of significant urban/industrial influences. The co (ppb) corresponding enhancement in CO and C2H2 and slight

Fig. 4. Variations in the vertical structureof (a) acetoneand (b)CO 2000 at four latitudes.Data are from missions19 (solid circle), 20 (open I I I I I square), 21 (open diamond), and 22 (open circle) representing Altltude>4km latitudesof 57øN, 52øN, 45øN, and 37øN,respectively. 600 i m mm ß (CO, NMHCs, NOy, and C2C14).Figure 5 showsthe latitudinal behavior of acetone, CO, and C2H2 in the free 200 ß tropospherefor altitudes above 4 kin. The CO and C2H2 mixing ratios are median values from a 5ø latitude band. It is evident that free tropospheric concentrations of all these 800 speciesare larger at the subpolarlatitudes. In large part this is due to the slower removal rates and the influence of 400 I I I t t northerly sourcessuch as fires. 35 40 45 50 55 60 65

Relationships Between Acetone and Selected Tracer and 150 m m m m m Oxidized Species Altltude>4km As has been previously stated,the measuredconcentration 120 of acetone showed significant variability above its geochemical background of 400-600 ppt. The relationship 90 between acetone and other primary and oxidized speciesis explored to get a better understandingof the nature of its sources. Figure 6 shows these correlations with select 60 C2H2 moleculessuch as C2H2, CO, C3H8, andC2C14. The first three are tracers of both urban and biomass-burningsources, while the last is purely indicative of urban/industrial 30 m m m m m pollution. Propane is also an eventual precursorof acetone. 35 40 45 50 55 60 65 The data are segregated to show mixing ratios in the Fig. 5. Latitudinaldistribution of acetone,CO, and C2H2 in the free boundarylayer (0-2 kin) and aloft (>2 kin). Figure 6 indicates troposphere.Data are from missions18-22 for altitudesabove 4 km. that a significant association between the variability of CO andC2H 2 data are medianmixing ratios within a 5ø latitudinal acetone and that of key speciesis present. These relation- band. 1810 SINGHET AL.: ACETONEIN THEATMOSPHERE

200 200 ! ! ! I I i I (a) R=0.70 R=0.75 (b) 160 160 o

120 120 =, øo o / l o o ß /o ß

8O 8O

o

4O 4O o o

I I I I i I I i

500 1000 1500 2000 25OO 500 1000 1500 2000 25OO Acetone (ppt) Acetone (ppt)

200 25 ! i ! I i i i !

R=0.79 (c) R=0.20 (d) 160 21

ß o o o o o o 120 17 o• o o oß 8O =' 0 •..,.'"'3:•• 13 - ß • ß (]DC•• .{:l• O O -- o o c•_..• c•c/•:/:)•o o o o 0 O0 0 •::) 0 CZ3•O CO 4O 9

I I I ! 5 i I I I

0 500 1000 1500 2000 2500 0 500 1000 1500 2000 25OO Acetone (ppt) Acetone (ppt) Fig.6. Relationshipof acetone with selected (CO, C2H 2, C3H8, and C2C14) tracers. Squares and circles represent data collectedbelow and above 2-km altitudes,respectively. enhancementin 03 are generallyconsistent with the combus- boundarylayer concentrationsare due to this exchangewith tion source of the . Fires were also visible in the water. As we shall discusslater, while water may act as a area and, in addition, aerosolswere significantlyenhanced reservoir of acetone, the possibility of acetone suggestinga young moist fire plume [Browell et al., 1991]. decompositionin water is unlikely. The generallow-level wind flow (associatedwith the poten- Urban/Industrialinfluences. Two examplesof acetone tial temperatureof 285 K) variedwith convergenceof trajec- levels in air influencedby urban/industrialsources are shown tories from the northerly and easterlydirections. A second in Figure 10. During mission16 (August9, 1990), which increasein acetoneat 4 km coincideswith C2C14increase wasintended as a marineair missionover the Atlantic,high and is suggestive of some urban contamination.Indeed, concentrations of acetone were encountered in the marine trajectoriesat the 305 K potentialtemperature level (= 3 km) boundary layer. These elevated acetone mixing ratios had a significantsouthwesterly component suggestive of coexistedwith highlevels of C2C14along with tracerspecies urban influences. suchas CO, NMHC, and NOy. The corresponding 03 mixing Figure9 showsthe verticaldistribution of acetone,C2C14, ratios were not significantly enhanced, suggestinga C2H2, and CO duringtransit flights from GooseBay (53øN) relativelyfresh plume and conditionsunfavorable for photo- to Frobisher Bay (63øN) and back (missions 18 and 19 on chemicalactivity. In this regardit is notedthat the boundary August13, 1990). Comparedto the boundarylayer, the free layer air had relativelycold temperatures(15ø-20øC) that are troposphericlevels of acetoneand othertracers (e.g., C2H2 generally not conducive to significant 0 3 synthesis. and CO)are enhanced without commensurateenhancement of Southwesterlytrajectories were consistentwith the view that C2C14 or of other anthropogenichalocarbons. Trajectory these air masses may have originated over the North analysesby Shiphamet al. [this issue]also showthe general Americancontinent [Shipham et al., this issue]. influenceof clean Arctic air duringthe entire flights. Near Figure 10 showsa secondepisode of pollutionthat was GooseBay the upperair masseshad high aerosollevels and encounteredin the free troposphereduring mission 17. High were probablyimpacted by biomass-burningplumes that had concentrationsof acetone and C2C14 were seen to coexist been somewhataged [Browellet al., 1991]. Figure9 acetone between3 and 6 km altitudesalthough a greatdeal of struc- distributionimplies a very cleanboundary layer decoupled ture was evident.At around3.5 km a layer containinghigh from a free troposphere.It is furthernoted that the very low ,03, and CO (>150 ppb) was seencoincident with boundarylayer concentrationswere also over large water highC2C14 and NOy concentrations. It is possiblethat the bodies. Acetone is highly soluble and substatialconcentra- plume layer between 3 and 4 km had some forest fire smoke tions in the water may exist. Most probably, the low mixed in it, while the 4- to 6-km layer was moredirectly SINGH ET AL.: ACETONE IN THE ATMOSPHERE 1811

8O I I i mentof 2.9 ppbNOy, 60 ppbCO, 1.2 ppbPAN, 0.07 ppb R(<2 k•)=0.$4 (a) 7O . R(),2 km)=0.34 o o C2C14,and 0.3 ppbC3H 8. Assumingthat this is a relatively • o oOO fresh and a typical urban plume, urban concentrations of 6O o%% acetone can be estimated by scaling up from the urban abundancesof known tracers. Typical urban mixing ratios 5O oo % g above the background levels can be determined from the 40 availableliterature to be 20-50ppb for NOy, 500-2000ppb

3O for CO, 0.2-0.5 ppb for C2C14,and 3-6 ppbfor C3H8. This o •o•O • • suggests that mean concentrations of acetone in polluted 2O • o• regions are only marginally elevated and may be in the 2- to 6-ppb range. It is noted that there was a striking difference 10 I I i i in the relative enhancement of industrial in air 500 1000 1500 2000 2500 massesthat had been significantly aged. For example, in two

lOOO I I i i instances (missions 16 and 17 shown in Figure 10) Aacetone/AC2C14 was found to be in the vicinity of 50-60 as R(<2 km)=0.78 (b) 800 . R(),2 km)=0.52 opposedto 3 in a fresh plume (mission 21). As we shall see in the next section, the most important source of acetone is o secondary in nature, and Aacetone/AC2C14 would increase 600 .. %0 0 • with the age of the air mass. The secondary sources,

ß however, may take many days to produce acetone and 400 - O0 (• 0 considerable dilution would have occurred. It is noted qbg • ß ß o however, that these estimated 2- to 5-ppb urban acetone o oooo ø o o 200 - o o ø..t mixing ratios are lower than the 12 (+4) ppb reported by m ß mø Snider and Dawson [1985] in Arizona but comparableto the m i I i 0.2- to 3- ppb levels reportedby Grosjean et al. [1990] from o 500 lOOO 15oo 2000 2500 several Brazilian cities. Isidorov [1990] reports of studies from West Berlin in 1977 where acetone mixing ratios as 600 m m m m high as 120 ppb were measured. In all of these cases, R(<2km)=0.45 (C) substantially different measurement techniques were 500 " R(),2km)=0.52 % o " employed. : 0 0 400 øoo o Sources,Sinks and Lifetimeof Acetone

300 .. o o% oOß - While the basic steps that determine the atmospheric 200 chemistry of acetone and its precursors are relatively well " •)o o •o o o o" o ß defined, its sourcesare not well understood.The job is made 100 " oo o •.Oo• ß ß . further difficult by the fact that very little atmosphericdata mm oOmm ß ßI ß m ß are available to constructits budget and the removal rates are both a function of season and latitude as acetone is removed 0 500 1000 1500 2000 2500 by reaction with free radicals, by photolysisand dry and wet Acetone (ppt) deposition. By using both photochemical models and measurements,we make a first attempt to develop a budget Fig. 7. Relationshipof acetonewith selectedoxidized species (03 , for acetone and compare our estimates of sourcesand sinks NDy,PAN). Symbols are same as in Figure6. to describe areas of uncertainties. impacted by urban transport. Trajectories at the 305 K and Sourcesof Acetone 315 K potential temperature level show that air masses originated in the Arctic and the Pacific oceans but accumu- Primary man-made emissions. There is little doubt that lated pollution during transit over northern United States and direct anthropogenic emissions of acetone are present. southern Canada [Global Tropospheric Experiment (GTE), Acetone is a commonly used solvent that is manufacturedin 1990]. large quantities. In the United States an attempt has been Although this study was not primarily designedto measure made to determine its stationary sourceemissions as part of polluted atmospheres,opportunities presented themselves to the NAPAP emissions inventory. Its aggregated emissions sample polluted air masseswhich indicatedevidence of fresh from use as a solvent and chemical intermediate in the United as well as aged contamination. During the return flight States are estimatedto be 0.2-0.25 Tg/yr [Middleton et al., (August 15, mission 22), acetone concentrations in the 1990]. Acetone has also been identified as a direct emission marine boundary layer, impacted by the east coast urban from automobiletail pipes [Sigsbyet al., 1987]. In a studyof plume, of 2.3 ppb were measured.A fresh urban plume was exhaust from 46 cars it was found that acetone emissions also sampled in the boundary layer during mission 21 from the tail pipe were highly variable and constituted10- (August 14, 2207 to 2210 UT). In this plume, levels of all 70% of the total aldehydefraction which in turn was 2-3% of urban tracers registered significant increases. An in-plume the total hydrocarbon emission (J. Sigsby, private enhancementof 0.2 ppb acetone coincided with an enhance- communication, U.S. EPA, 1991). From these studies one 1812 SINGHET AL.: ACETONEIN THE ATMOSPHERE

C2Cl4 (ppt) CO (ppb) NOy(ppt) 0 10 20 30 40 50 40 80 120 160 200 500 1000 1500 6 I I I I I I i • (a) (b) (c)

[] rq[] [] Acetone NOy 4 [] []

_ [] 03

C2CI4[•] co

500 1000 1500 2000 2500 50 70 90 110 130 150 0 10 20 30 40 30 60 70 80 Acetone (ppt) C2H2 (ppt) 0 3 (ppb) Fig.8. Evidenceof acetoneenhancement in a forest fire plume on August5, 1990(mission 13). C 2C14 distribution is usedto rule out significantindustrial pollution. can estimate that on the average about 1% of the exhaust (CH3)2CH2 + OH + (02) -->CH3CHO2CH 3 + H20 (80%) emissionis acetone.In the United States,total hydrocarbon -->CH3CH2CH202 + H20 (20%) emittedfrom mobilesources are in the vicinityof 6-7 Tg/yr CH3CHO2CH3+NO+(O2) -->CH3COCH3+NO2 + HO2 [Singh and Zimmerman, 1992]. Thus an acetoneauto exhaust CH3CH2CH202+NO+(O2) -->CH3CH2CHO + NO2+HO2 source of 0.05-0.1 Tg/yr can be estimated for the United CH3CHO2CH3 + HO2 -->CH3CHOOHCH3 + 02 States. Extrapolationto the world suggeststhat 0.6-0.8 CH3CHOOHCH3 + hv -->CH3CHOCH 3 + OH Tg/yr and 0.2-0.3 Tg/yr of acetone are emitted from CH3CHOCH3 + 02 -->CH3COCH3 + HO2 stationaryand mobile sources,respectively. Secondarysources of acetone. As hasbeen suggested by Thus acetoneis a productof propaneoxidation both in Singhand Hanst [1981], nearly80% of propaneon a high and in low NOx environments.The above mechanism basis is oxidized by OH radicalsto produceacetone; the actually applies to any alkane with a similar structure remainder20% producingpropionaldehyde. The following (CH3CHRCH 3) whereR is an alkyl group.In the real world mechanismshows the formationof acetonefrom propane. the mostimportant candidates in this categoryare propane,

C2Cl4 (ppt) CO (ppb) 0 10 20 30 40 50 0 40 80 120 160 6 I I I I I I ! (a) (b) ß d,,

4 O O ß ß ll onto C2H2o o ß ODe O . e D D 0 o0 Acetone o o ß o o .

CO C2CI4DI• D . I

&*, d& I 0 500 1000 1500 2000 2500 0 50 100 150 200 250 300 Acetone(ppt) C2H2 (ppt)

Fig. 9. Acetoneand tracer mixing ratios present in the troposphereon August13, 1990(missions 18 and 19 ). Data werecollected during to andfrom transit between Goose Bay (53øN)and Frobisher Bay (63øN). SINGHET AL.' ACETONEIN THEATMOSPHERE 1813

C2CI4 (ppt) NOy(ppt) 10 15 20 25 30 35 0 100 200 300 400 500 I I I I I I I I (a) (b)

I Mission 16 _ ß _

[• ission16 _ / I C2CI4I':-II • _• NOy '[:]• e• -- [• - _ • • 03 1

I

- , 500 1000 1500 2000 2500 20 40 60 80 lOO Acetone (ppt) Ozone (ppb)

C2CI4 (ppt) NOy(ppt) 5 10 15 20 25 30 35 140 280 420 560 700 6 I I I I I I I I I (c) (d) ß

NOy ß • • - Acetone

!

Mission 17 Mission 17

I I I I I I I I 0 400 800 1200 1600 2000 0 20 40 60 80 100 Acetone(ppt) Ozone(ppb)

Fig. 10. (a andb) Evidencefor acetoneenhancement within a pollutedair massin theboundary layer (mission 16, August9, 1990)and (cand d) thefree troposphere (mission 17, August 11, 1990).C 2C14,0 3, andNOy distributions are also shown. isobutane,and isopentane[Singh and Zimmerman,1992]. The certain but can be expectedto be in the 1-2 Tg/yr range. globalsource of propanehas beenestimated to be 15-20 Thus thesealiphatic hydrocarbons alone can produce17-23 Tg/yr basedon direct atmosphericmeasurements and its Tg/yr of acetone. calculatedremoval rate. Known sourcesadd up to only about Alkanes are not the only hydrocarbonsthat can to 5 Tg/yr and large unknown sources (probably significantacetone formation. Many alkenes,both natural natural/biogenic)are presumedto exist. This 15-20 Tg/yr and man-made,also lead to acetoneproduction. The follow- propanesource has the potentialto produce16-21 Tg/yr of ing reactionsshow the oxidationof isobutenewith OH and acetone. Emissions of isobutane and isopentane are less 0 3 leadingto the formationof acetone. 1814 SINGH ET AL.: ACETONE IN THE ATMOSPHERE

(CH3)2C=CH2+OH+ (02) --> (CH3)2C(O2)C(OH)H2 1200 I I I I (CH3)2C(O2)C(OH)H2 + NO--> CH3COCH3 + HOCH2 +NO2 (CH3)2C=CH2 + 03 --> Criege --> CH3COCH3+ 1000 - R=0.89 - O2CH2 800 In many studies involving , acetone has been identified as a product of C4-C 6 oxidation [NAS, 600 1976]. Indeed, any with a structure similar to (CH3)2=CR 2 is a potential sourceof acetone.Of course,as 400 ß ß these molecules get more and more complex, competing reactions will cause the yields of acetoneto drop. It is esti- 200 mated that isobutene and other similar alkenes can result in o o o the formation of about 2-3 Tg/yr of acetone. I ß I I I The above discussion also applies to natural molecules which have structures similar to (CH3)2=CR 2. The most 0 500 1000 1500 2000 2500 abundant of these is probably myrcene. Myrcene has been Acetone (ppt) identified as an emissionfrom a variety of plants and vegeta- Fig. l l. Relationshipbetween mixing ratios of acetoneand isoprene tion and is often present in measurableatmospheric concen- in the boundarylayer (0-2 km, 45ø-65øN). Data are for overlapping trations [Isidorov et al., 1985; $ingh and Zimmerman, 1992]. measurementsmade during missions13-22. The circles representdata Basedon emissionstudies of deciduous,evergreen, and mixed points where the air was heavily influenced by urban pollution forests, J. Greenberg and P. Zimmerman (NCAR, Boulder, (mission 21) and smoke plumes (mission 13). Colorado, private communication, 1992) find that myrcene emissions range from 0 to 5% of those of •-pinene. The primary productivity) is considered to be a reasonable lowest myrcene emissions appear to be from evergreen estimate for the globe. Assuming that the lowest emission forests. Plant species such as Scots pine have been found to rate is representativeof plants associatedwith 80% of CO2 produce significantly higher emissions of myrcene. uptake and the highest rate, typical of evergreens,associated Assuming a 200 Tg/yr global source of •-pinene, myrcene with 20% of CO2 uptake, an acetoneglobal sourceof 9 Tg/yr emissions can be estimated to be about 5 Tg/yr. Chamber can be calculated. Assuming the lowest emission rate to be studiesof Arnts and Gay [1979] suggestthat 4% of myrcene representativeof all vegetation, a 4 Tg/yr sourceis possible. carbon may be converted to acetone. This yield may be on To further explore the existence of biogenic sources of the low side because many intermediates that may produce acetone we compared its atmospheric behavior during acetone can be lost to chamber walls. Assuming a 4% yield ABLE3B with that of a well-known biogenic hydrocarbon, from myrcene, an acetone source of about 0.2-0.3 Tg/yr can namely, isoprene. Figure 11 shows the relationship between be calculated. measuredisoprene and acetonemixing ratios for the overlap- A much larger but much more uncertain source of acetone, ping periods during ABLE3B. Since isoprene was rarely from the OH oxidation of •-pinene, has been proposedin an measured in the free troposphere,these data are from the unpublished work by Gu et al. (1984). In their laboratory boundary layer only (0-2 km). The three outlier data points studies they find that 15 (+10)% of •-pinene by mole is are shown as circles as they represent conditions where the converted to acetone. Assuming that about half the •-pinene air sample was strongly influenced by an urban plume is removed by reaction with OH, a large source of acetone (mission 21) or a smoke plume (mission 13). While the (6+4 Tg/yr) can be calculated.Unfortunately, no independent available data are limited, Figure 11 is strongly suggestive corroboration of this result can be found in the published of the biogenic sourcesof acetone in the sampled region. It literature. Recent attempts to identify acetone as a product of is certainly plausible that direct biogenic emissions of •-pinene oxidation have been unsuccessful (R. Atkinson, acetone are significant. A great deal more researchis needed private communication, 1992). Clearly more definitive work to understand its biochemistry and to have meaningful is needed to ascertain or rule out this potentially important quantitative data on its biogenic emissions. pathway. Biomass burning source. The sampledarea was impacted Direct biogenic emissions. Acetone has been identified as by local and distant fires burning over the Hudson Bay a direct biogenic emission from a large number of plants. In lowlands and over Alaska [Shipham et al., this issue]. one study, 22 plant species characteristicof northern hemi- Acetone has not yet been identified as a direct emission from sphere forests were studied for organic emissionsand acetone fires. However, these field data (e.g., Figure 8) leave little was found to be emitted in all cases [Isidorov et al., 1985]. doubt that this indeed is the case. Acetone in instances where Recent studies in the United States (P. Goldan and R. Falls, fire plumes were sampled was clearly elevated along with NOAA, Boulder, Colorado, private communication, 1992) other speciessuch as CO and C2H 2. By carefully analyzing have also seen these emissionsin a variety of rural locations measurements within fire plumes, a Aacetone/ACO(v/v) in southeasternUnited States. It appears that evergreens are = 0.025 (0.02-0.03) could be calculated. This acetone the most productive source of acetone and the least enhancementwas probably an upper limit as some formation productive sourcesof myrcene. These investigatorshave also of acetone from hydrocarbon oxidation may already have performed limited laboratory studies to evaluate emission occurredwithin the sampledplumes. The same plumes had a fluxes. In laboratory studies with Colorado blue spruce, AC2H2/ACO ratio in the vicinity of 0.001-0.002 in near Alberta spruce, loblolly pine, and aspen, acetone emissions agreementwith results from studiesover Alaska [Wofsy et al., weredetermined to be 2.10-4 to 3.10-5 g acetone(C)/gCO2 1992]. It is further noted that the overall mean correlation of (C) uptake.A CO2 plantuptake of 9 (+2).1016g(C)/yr (gross acetone and CO is also linear with a slope of 0.03 (Figure SINGH ET AL.: ACETONE IN THE ATMOSPHERE 1815

6a) suggestingthat much of the acetone-CO correlation is probably dictated by the influence of fires in the region. 7 [:. \ April1// • 55øN( Assuming a CO source from biomassburning of 200 Tg/yr / \ / [Lobert et al., 1991], and a Aacetone/ACO of 0.025, an i ß : / acetone source of 10 (8-12) Tg/yr can be calculated. Clearly more work needs to be done to better quantify this source, • '. \ I Jan1 but preliminary results from this study suggestthat acetone •), '. .... :\ ;I o.,y • ,, is a significantproduct of biomasscombustion. • 3 - ; '. '• • ' Sinks and atmospheric lifetime of acetone. Acetone ; /. , photolysis and its reactions with OH are probably its major loss pathways.Acetone is capableof producingfree radicals '., 1 ., • '..'9(•. (j•y•) and intermediate oxygenates. Among the many products of ", % .'. % acetone oxidation are PAN, acetic acid, peroxyacetic acid, ß i i ß ß ß iii ß ß i ß ß ß i i methyl glyoxal, and complex peroxides. More detailed 10 100 1000 chemistry is provided elsewhere [Singh and Hanst, 1981; Acetone lifetime, days Henderson et al., 1989; Kanakidou et al., 1991], but the following are some of the salient chemical steps in the 100 I' I I I atmosphericdecomposition of acetone: ,.,,•'" (b) CH3COCH3+hv+(O2) --->CH3COO2+CH 3 A 8O - JULY1 0.9k% ..'/ - CH3COCH3+OH+(O2) -->CH3COCH202+H2 ¸ / CH3COO2+NO2 •-> CH3COO2NO2 (PAN) ß CH3COO2+HO2 --->CH3COO2H+O2(67% ) - ./ - --->CH3COOH+O3(33%) " 3.5km CH3COCH202+HO2 --> CH3COCH2OOH+O2 ,.=_ 40 CH3COCH202NO+(O2) --->HCOCOCH3+NO2+HO 2 i m•l•l•m• 1 CH3COCH2OOH+hv -->CH3COCH20+OH

A lesser amount of removal may also occur through wet m "•.•••••,.•.• •'• 7. krn and dry deposition. Although acetone is highly water I I I I soluble, its partition coefficient strongly favors the gas phase(H = 32 M atm-1 at 25øC)and there appears to beno 15 30 45 60 75 90 known mechanism for hydration and significant photolytic Latitude o N loss in aqueousmedium [Chatfield et al., 1987; Betterton, Fig. 12. (a) Calculatedatmospheric lifetime of acetoneas a function 1991]. The possibility of acetone loss by microbial of seasonand height at 55øN and (b) as a function of latitude and processesafter dissolutionin seawatercannot be ruled out. height for July 1. Lifetimes are based on two-dimensionalmodel Based on present information, it appears that gas phase calculationswith removal by photolysisand reaction with OH only. losses are favored and removal by any process involving In (a)the lifetime (for July 1) due to photolysis(hv only)and OH dissolution should be small. Seawater algae may also provide (OH only) is also shownseparately . a small marine source of acetone [Whelan et al., 1982]. No direct measurements of acetone in seawater are available, but essentialequilibrium with the atmosphericabundance can be dimensional and three-dimensional models of the atmosphere expected. were used [Kanakidou et al., 1991, 1992]. In both of these We have used a two-dimensionalphotochemical model to models the only source of acetonewas that resulting from calculate acetone lifetimes based on photolysis and OH propaneoxidation. The chemicalscheme used in both two- removal alone. Absorption cross sectionsused are those of dimensional and three-dimensionalmodels described the 03- Emrich and Warneck [1988] and the OH field is consistent OH-NOx-CO-CH4-C2H6 andC3H 8 chemistry[Kanakidou et with a methyl chloroformatmospheric lifetime of 6.2 years. al., 1991]. The model calculationsincorporated seasonal and Details of the nature of these two-dimensional calculations vertical resolution for the OH and the UV field as well as a have already been describedby Kanakidou et al. [1991]. measureof dry deposition.The depositionvelocity (V d) of Figure 12a shows these calculatedatmospheric lifetimes at acetoneis probablyextremely small and may be negligible 55øN. In summer(July 1), acetonelifetime is calculatedto be [Wesely, 1989]. In the three-dimensional model run, a 10-30 days with OH removal dominating in the boundary uniform depositionvelocity of 0.05 cm/s, typical of similar layer and photolysis dominating in the free troposphere. species,was appliedfor acetone.In thesemodel runs, nearly This lifetime is significantly longer in other seasons 64% of acetonewas removed by photolysis,24% by reaction approaching 1-3 months in April and 6-36 months in with OH, and the remaining12% by dry deposition.A global January. Figure 12b shows the dependenceof acetonelife- mean lifetime of acetone of about 16 days was derived from time (July 1) with latitude and height. As can be expected the three-dimensional model. The three-dimensional model from the OH and UV distribution in the atmosphere,the - required a global propane source of 17 Tg/yr to fit the time of acetone is substantially shorter in the tropics, propanebudget: 12 Tg of this sourceis distributedaccording approaching 10-20 days. to NOx industrialemissions, 1 Tg is assumedto be emitted To ascertain the sink strength of acetone both two- by tropical biomassburning, 2 Tg from plants, and 2 Tg 1816 SINGH ET AL.' ACETONE IN THE ATMOSPHERE

lOO I i 16.511.9 9.2

IOO 7.2

f•

4.2 "• 65 ø W (August 1) El

7oo 3.0 5O 100 1.9 25O

1.0

lOOO 75 55 35 15 0 15 35 55 75 lOO i 16.5

11.9

9.2

7.2

5.6 f•

- Zonalmean (August 1 5• 4.2

i 7oo 3.0

1.9

1.0

I I , • I • I I I lOOO --(b) • I , I 2••25•)t 0 75 55 35 15 o 15 35 75 South I.mtitud© North

Fig. 13. Calculated atmospheric distribution of acetone for August 1 based on a three-dimensional model of the troposphere.(a) The isoplethsshow acetonemixing ratios (ppt) as a function of latitude for 65øW longitude and (b) for zonal mean conditions. The acetone source is exclusively due to propane oxidation and a uniform acetone deposition velocity of 0.05 crn/sis used.A 17 Tg/yr propanesource, as describedby Kanakidouet al. [1992] is employed.

from oceans [Kanakidou et al., 1992]. An 18 Tg/yr global between 35 ø and 65øN, a true background concentration of acetone source is generated from this propane oxidation in acetone in this region was 500-600 ppt. Earlier, more the model. On an annual basis, 90% of this source is in the limited data of Penkett from 35øN suggests a similar northern hemisphere (NH). In the NH, maximum values of background level. Scaling up the model results at least for acetone are computed for February and minimum values for the NH would suggestthat a global acetone source of 40-60 the end of July when photochemicaldestruction of acetone is Tg/yr would be consistentwith these NH measurements.This near its peak. estimate assumes that all acetone sources have a distribution Figures 13a and 13b show the model-deriveddiurnal mean similar to the source resulting from propane oxidation. acetone abundance for 65øW longitude and zonally mean conditions for August 1 as a function of latitude and height. AcetoneGlobal Budget The relatively short lifetime of acetoneand its precursors,of the order of a few weeks, results in sharp latitudinal and Table 3 summarizes all the sources that have been longitudinal gradients. The meridional distribution of the quantified above in a rough fashion. Although substantial zonal mean acetone concentration is relatively regular uncertainties exist, an acetone global source of about 40 decreasing with latitude and height. In the southern hemi- Tg/yr probably exists. Nearly half of this source is as a sphere (SH) an acetone zonal mean concentration of 20-40 result of oxidation of NMHC with propane being the ppt is calculated for August. A model-distributed global dominant precursor.Substantial biogenic (20%) and biomass photochemical acetone source of 18 Tg/yr results in about burning (25%) sources are estimated. At present it appears 200 ppt background acetone concentration in the lower that the atmosphericacetone abundance and its removal rates troposphereat 55øN in August. Based on actual measurements would be compatible with a global acetone source/sinkof SINGH ET AL.: ACETONE IN THE ATMOSPHERE 1817

TABLE 3. Global Sources and Sinks of Acetone

Global Annual SourceT•,pe Emissions,T•/yr Comment Primary anthropogenic =95%NH Stationary sources 0.5 (0.4-0.7) extrapolated Mobile sources 0.3 (0.2-0.3) from U.S. data Primary biogenic 9 (4-18) =60%NH, poorly quantifiable Secondary anthropogenic =80%NH And biogenic propane oxidation 17 (15-20) isobutane/isopentaneoxidation 2 (1-3) isobutene/isopenteneoxidation 1 (1-2) myrcene oxidation 0.2 (0.2-0.3) a-Pinene oxidation* --- highly uncertainchemistry Biomass burning 10 (8-12) from this study, =80%SH Total Sourcestrength 40 (30-46) =60%NH;40%SH

Totalsink strength + 40-60 2D/3D model calculation

NH, northernhemisphere; SH, southernhemisphere. *A largeacetone source (=6 Tg/yr)may be postulatedfrom the oxidation of a-pinenebased on the kinetic study of Gu et al. (1984). No independentverification of this result has been possible. +Sinkestimate is basedon scalingup of modeloutput to fit measurementsat 55øN. In themodel used, acetone loss is due to photolysis(=64%), OH reactions(=24%), and dry deposition(=12%).

40-60 Tg/yr. However, this calculation is constrained by 2% at 280øK (=2 km), 10% at 270øK (=4 km), and 100% at rather limited atmospheric data largely collected from the 250øK (=7 km). The higher yield of PAN with altitude is due northern hemisphere in one season. Based on estimates to the greater thermal stability of PAN at lower temperatures shown in Table 3, the source-sinkrelationship for acetoneis and to the fact that photolyric decompositionrate of acetone roughly in balance but the uncertaintiesare quite large and in increases with altitude [Kanakidou et al., 1991]. These zero- many cases unquantifiable. Clearly a body of atmospheric dimensionalcalculations suggest that in the middle and upper data that defines the seasonal, vertical, and latitudinal distri- troposphere, 100-500 ppt of PAN may result from acetone bution of acetone is needed. Much more accurate information photolysis alone. Needless to say, vertical mixing and on the direct emissions of acetone from vegetation and advectionwould tend to reducethe actual yield of PAN. biomass are required to further improve the Three-dimensional model runs were made to more budget of acetone.It is possiblethat atmosphericabundances accurately address the role of acetone in PAN formation. of acetonecan also be derived from the Jungfraujochspectra Model results showed that in the high northern latitudes [Ehhalt et al., 1991] and this possibility should be further (55øN) for August, the contributionof the calculated acetone explored. (=200 ppt) to the zonal average PAN concentrationis 40-50 ppt in the middle and upper troposphereand lower (=10 ppt) AcetoneAs a Sourceof Peroxyacetylnitrate(PAN) near the surface. Scaling up to the measured concentrations of acetone (500-1000 ppt) one can estimate that some 100 Singh and Hanst [1981] have proposedthat photolysis of to 200 ppt of the middle/upper troposphericPAN may have acetone produces peroxyacetyl radicals which can lead to resulted from acetone oxidation alone. It is reasonable to PAN formation. A zero dimensionalmodel as used by Singh postulatethat acetone was probably a major PAN precursor and Hanst [1981] and new rate constantsas presentedby over northeasternCanada during ABLE3B [Singh et al., this Dernore et al. [1992] and Kanakidou et al. [1991] have been issue] and would play an important role everywhere if used to further evaluate this possibility in light of these new substantialconcentrations are found to be globally present. acetone measurements. The basic chemical mechanism is describedas follows with a steadystate solutionfor PAN. CONCLUSIONS

CH3COCH3 + hv + (02) -") CH3COO2+CH3 (JA) Acetone, an oxygenated organic hydrocarbon, has been CH3COO2 +NO2 <--)CH3COO2NO 2 (PAN) (k 1, found to be the dominant nonmethane organic species present in the subarctic atmospheresampled during ABLE3B. CH3COO2 +NO ---) CH3 + CO2 + NO2 (k2) A substantialglobal source in the vicinity of 40-60 Tg/yr is PAN+ hv --) Products (Jp) estimated to be present. It is suggestedthat nonmethane PAN + OH --) Products (k3) hydrocarbon oxidation, biomass burning, and direct biogenic emissionsare important sourcesof acetone.Insufficient data [PAN]ss=JA[CH3COCH3]/{(I+k2[NO]/kl[NO2])(k31OH]+Jp) are available to reliably quantify these source strengths.By +k_1 k2[NO]/k 1[NO2] } using atmosphericdata and photochemicalmodels, a rough atmosphericbudget of acetonehas been presented.While the Using available kinetic data, the above equation can be source-sink equation appears to be roughly balanced, much used to calculate steady state PAN mixing ratios for typical more atmospheric and source data are needed to reliably atmosphericconditions and acetone abundances.These, as a estimate these relationships. Atmospheric abundance of percentageof acetonemixing ratio, are calculatedto be about acetone is expected to have strong latitudinal and seasonal 1818 SINGH ET AL.: ACETONE IN THE ATMOSPHERE

variations, but no direct observations are available. The Isidorov, V. A., I. G. Zenkench, and B. V. Iofe, Volatile organic possibility of deriving acetone abundancesfrom atmospheric compoundsin the atmosphereof forests,Atmos. Environ., 19, 1-8, 1985. spectra(such as the Jungfraujochspectra) should be explored. Kanakidou, M., H. B. Singh, K. M. Valentin, and P. J. Crutzen, A It is postulatedthat acetone photochemistrymay be respon- two-dimensionalmodel study of ethane and propane oxidation in sible for a significant fraction of the observed free the troposphere,J. Geophys.Res., 96, 15,395-15,413, 1991. troposphericPAN. Oxygenated molecules are important com- Kanakidou, M., P. J. Crutzen, P. H. Zimmermann, and B. Bonsang, ponents of the atmosphere even though very little about A three dimensional global study of the of ethane and propane in the troposphere:Production and transport their sources and fate is known. of organic nitrogen compounds,in Modelingand its ApplicationIX, edited by H. van Dop and G. Kallos, pp. 415-426, Acknowledgments. This research is supported by the NASA Plenum, New York, 1992. Global Tropospheric Experiment. We acknowledge all ABLE3B Kasting, J. F., and H. B. Singh, Nonmethane hydrocarbonsin the participants for their cooperationand support. Special thanks are due troposphere: impact on odd and odd nitrogen to the flight and groundcrew of the Wallops Electra for making this chemistry,J. Geophys.Res., 91, 13,239-13,256, 1986. effort a success.Computational assistanceprovided by B. Sitton of Lobert, J. M., D. H. Scharffe, T. A. Kuhlbusch, R. Seuwen, and P. J. Synernet Corporation and W. Viezee of SRI-International is greatly Crutzen, Experimentalevaluation of biomass burning emissions: appreciated.M. Kanakidou expressesgratitude to the CEA and the Nitrogen and carbon containing compounds,in Global Biomass CNRS for support. Burning, edited by J. S. Levine, pp. 289-304, MIT Press, Cambridge, Mass., 1991. Loyd, A., Troposphericchemistry of aldehydes,NBS Spec. Pub. U. REFERENCES S., 557, 27-48, 1979. Middleton, P., W. Stockwell, and W. P. Carter, Aggregation and Arnold, F., G. Knop, and H. Zeiereis, Acetone measurementsin the analysis of volatile emissions for regional upper troposphere and lower stratosphere-implicationsfor modeling,Atmos. Environ., 24(A), 1107-1133, 1990. hydroxyl abundances,Nature, 321, 505-507, 1986. National Academy of Sciences (NAS), Vapor-Phase Organic Arnts, R. R., and B. W. Gay, Jr., Photochemistryof some naturally Pollutants: Volatile Hydrocarbonsand Their Oxidation Products, emitted hydrocarbons,EPA-600/1-79-081, Environ. Prot. Agency, National Academy of SciencesPress, Washington, D.C. Washington, D.C., 1979. O'Hara, D., and H. B. Singh, Sensitive gas chromatographic Atkinson, R., Gas phase tropospheric chemistry of organic detection of acetaldehydeand acetone using a Reduction Gas compounds:A review, Atmos.Environ., 24(A), 1-41, 1990. Detector, Atmos. Environ., 22, 2613-2615, 1988. Betterton, E. A., The partition of ketones between the gas and Penkett, S. A., Non-methane organics in the remote troposphere, aqueousphases, Atmos.Environ., 25(A), 1473-1478, 1991. AtmosphericChemistry., edited by E. D. Goldberg, pp. 329-355, Browell, E., et al., Air mass characteristics observed over Canada Springer-Verlag,New York, 1982. during ABLE3B field experiment(abstract), Eos, Trans. AGU, 72 Robinson, E., R. A. Rasmussen, H. Westberg, and M. Holdren, (17), Spring Meeting supp]., 73, 1991. Nonurban nonmethane low molecular weight hydrocarbon Cavanagh, L., C. Schadt, and E. Robinson, Atmospheric concentrationsrelated to air mass identification,J. Geophys.Res., hydrocarbonand measurementsat Point Barrow, 78, 5345-5351, 1973. Alaska, Environ. Sci. Technol., 3, 251-257, 1969. Shepson, P. B., D. Hastie, and H. Schiff, Atmospheric Calvert, J. G., and S. Madronich, Theoretical study of the initial concentrations and temporal variations of C1-C3 carbonyl products of atmosphericoxidation of hydrocarbons, J. Geophys. compoundsat two rural sites in central Ontario, Atmos.Environ., Res., 92, 2211-2220, 1987. 25(A), 2001-2015, 1991. Chatfield, R. B., E. P. Gardner, and J. G. Calvert, Sources and sinks Shipham, M. C., A. Bachmeier, D. Cahoon, Jr., G. Gregory, E. of acetone in the atmosphere:Behavior of reactive hydrocarbons Anderson,and E. Browell, A meteorologicalinterpretation of the and a stable product atmosphere,J. Geophys.Res., 92, 4208-4216, Arctic Boundary Layer Expedition (ABLE)3B flight series, J. 1987. Geophys.Res., this issue. Demore, W. B., et al., Chemical kinetics and photochemicaldata for Sigsby, J. E., S. Tejada, W. Ray, J. M. Lang, and J. W. Duncan, use in stratosphericmodeling, JPL Publ. 92-20, 1992. Volatile organic compoundemissions from 46 in-use passenger Duce, R. A., V. A. Mohnen, P. R. Zimmerman, D. Grosjean, W. cars, Environ. Sci. Technol., 21,466-475, 1987. Cautreels, R. Chatfield, , R. Jaenicke, J.A. Ogren, E.D. Singh, H. B., and P. L. Hanst, Peroxyacetyl (PAN) in the Pellizzari, and G.T. Wallace, Organic material in the global unpolluted atmosphere: An important reservoir for nitrogen troposphere,Rev. Geophys.,21, 921-952,1983. , Geophys.Res. Lett., 8, 941-944, 1981. Ehhalt, D. H., U. Schmidt, R. Zander, P. H. Demoulin, and C. P. Singh, H. B., and J. F. Kasting, -hydrocarbon Rinsland, Seasonal cycle and secular trend of the total and photochemistry in the marine troposphere and lower troposphericcolumn abundanceof ethane above the Jungfraujoch, stratosphere,J. Atmos.Chem., 7, 261-285, 1988. J. 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Atmos.Chem., 8, 277-298, compoundsin macroalgae,Nature, 299, 50-52, 1982. 1989. Wofsy, S. C., et al., in the Arctic and Isidorov, V. A., Organic Chemistry of the 's Atmosphere, subarctic: Natural fires, mid-latitude industrial sources, and Springer-Verlag, New York, 1990. stratosphericinputs, J. Geophys.Res., 97, 16,731-16,746, 1992. SINGH ET AL.: ACETONE IN THE ATMOSPHERE 1819

M. Kanakidou, Centre des Faibles Radioactivites, Laboratoire D. R. Blake, University of California, Irvine, CA 92717. mixte CNRS/CEA, F-91198 Gif-sur-Yvette, France. D. Bradshaw,Georgia Institute of Technology,Atlanta, GA D. O'Hara, San Jose State University Foundation, Moffett Field, 30332. CA 94035. P. J. Crutzen, Max Planck Institute for Chemistry,D-6500 Mainz, W. Sachse,NASA Langley ResearchCenter, Hampton, VA 23665. Germany. D. Herlth and H. B. Singh, NASA Ames ResearchCenter, Moffett (Received March 7, 1992; revised March 15, 1993; Field, CA 94035. accepted March 15, 1993.)