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2384 J J Ensberg et al Impact of vehicular emissions on SOA. atmosphere the procedures we use to analyze these issues Volkamer 2010 Concentrations of submicron nonrefrac. are likely to be applicable to major urban areas worldwide tory nrPM1 organic aerosol particles were measured us. Based on the highly resolved speciation profiles of gasoline ing an Aerodyne high resolution time of flight aerosol mass. and diesel fuel Gentner et al 2012 estimated that diesel spectrometer hereinafter referred to as AMS DeCarlo. exhaust is responsible for 2 7 times more SOA than gasoline et al 2006 The OA mass spectral matrix was deconvolved. exhaust in California However from measurements of the into components using PMF a receptor based factorization. weekday weekend cycle of organic aerosol black carbon model Paatero et al 1994 The OA organic aerosol com. single ring aromatic hydrocarbons CO and oxides of nitro ponents from the PMF positive matrix factorization analy. gen NOx NO NO2 in the Los Angeles L A Basin sis were identified by their mass spectra diurnal cycles and. Bahreini et al 2012 and Hayes et al 2013 conclude that elemental composition as well as by the concentration ra. emissions from gasoline fueled vehicles dominate the SOA tios and correlations of their time series with tracers These. budget Notably the conclusions of Bahreini et al 2012 components are 1 hydrocarbon like organic aerosol HOA. and Hayes et al 2013 are based on the observation that 2 cooking influenced organic aerosol CIOA 3 local or. diesel activity has a clear weekday weekend cycle whereas ganic aerosol LOA 4 semi volatile oxygenated organic. measured CO mixing ratios and the enhancement of SOA aerosol SV OOA and 5 low volatility oxygenated organic. with respect to CO exhibit virtually no weekday weekend aerosol LV OOA The HOA component has been previ. cycle when segregated by photochemical age Nevertheless ously described as a surrogate for primary combustion OA. as acknowledged by Hayes et al 2013 the conclusions and the SV OOA and LV OOA components as surrogates for. of Bahreini et al 2012 and Hayes et al 2013 presume fresher and aged SOA respectively Zhang et al 2007. that vehicular emissions are the dominant source of anthro Aiken et al 2008 Jimenez et al 2009 Ulbrich et al 2009. pogenic fossil SOA in the L A Basin As discussed in Hayes et al 2013 the LOA component ex. hibits high frequency fluctuations most likely resulting from. local sources in close proximity to the Pasadena ground site. 2 Ambient measurements However since LOA represents only 5 of the total OA. budget this factor is not considered further, Ambient data CO NOx NOy O3 OH VOCs submi Figure 1 shows measured PMF factor concentrations nor. cron nonrefractory nrPM1 organic aerosol at the Pasadena malized by CO enhancement 1CO is the difference between. ground site were collected during the 2010 CalNex experi the ambient CO and the estimated background CO 105 ppb. ment Ryerson et al 2013 The CalNex Pasadena ground as functions of photochemical age see Hayes et al 2013. site was located 18 km northeast of downtown Los An for a detailed description of how this figure was constructed. geles on the California Institute of Technology Caltech The photochemical age of the air mass over the Pasadena site. campus in Pasadena California 34 1406 N 118 1225 W was calculated by two methods 1 from the ratio of 1 2 4. 236 m a m s l The measurement period was 15 May 2010 trimethylbenzene to benzene concentrations as described in. 00 00 16 June 2010 00 00 local time The prevailing wind Parrish et al 2007 and 2 by defining the photochem. direction during daytime in Pasadena was from the south ical age as log10 NOx NOy similar to Kleinman et al. west due to the sea breeze which brought air masses from 2008 Both methods give very similar results and all pho. the Pacific Ocean across central Los Angeles to Pasadena tochemical ages were calculated for reference using an aver. CO concentrations were measured by two vacuum UV age OH radical concentration of 1 5 106 molecules cm 3. resonance fluorescence instruments AL5001 AL5002 For reference the daily day and night OH radical concen. Aerolaser Gerbig et al 1999 CO emissions in Los tration averaged over the entire campaign at the Pasadena. Angeles are attributable almost exclusively to vehicu site was 1 3 106 molecules cm 3 Note that the OH expo. lar emissions Griffin et al 2007 http www arb ca gov sure which is fully constrained by the measured evolution. app emsinv emssumcat php with minor contributions from of the benzene trimethylbenzene ratio is the only quan. cooking and oxidation of biogenic emissions Hayes et al tity needed for calculating the fraction of VOC that has re. 2013 Allan et al 2010 A Fluorescence Assay by Gas Ex acted e g frac 1 exp k OH exposure Therefore. pansion FAGE instrument was utilized to determine the OH choosing a different OH radical concentration will not in. concentration Dusanter et al 2009 The concentration of fluence our results because the OH exposures remain the. O3 was measured by UV differential absorption 49c Ozone same Owing to the formation of SOA the OOA factors. Analyzer Thermo Scientific An in situ Gas Chromatogra are enhanced increased with respect to 1CO as the pho. phy Mass Spectrometry GC MS instrument provided the tochemical age of the air mass increases As shown in. mixing ratios for a variety of VOCs Gilman et al 2009 Fig 1b the enhancement of OOA SV OOA LV OOA rel. NOx and NOy concentrations were measured using chemilu ative to 1CO after 0 45 days of photochemical processing. minescence 42i TL with Mo converter Thermo Scientific is 48 g OOA sm 3 ppmv CO 1 48 is the difference be. and NO2 was measured with Cavity Enhanced Differential tween 58 which occurs at 0 45 days and 10 which oc. Optical Absorption Spectroscopy CE DOAS Thalman and curs at 0 days whereas the ratio of POA HOA CIOA to. Atmos Chem Phys 14 2383 2397 2014 www atmos chem phys net 14 2383 2014. J J Ensberg et al Impact of vehicular emissions on SOA 2385. 3 Results and discussion,3 1 Emission ratios and required SOA yields. Fuel sales data reported by the California Department. of Transportation http www dot ca gov hq tsip otfa tab. documents mvstaff mvstaff08 pdf indicate that diesel and. gasoline fuel sales in all California counties upwind of. Pasadena during 2010 represented approximately 13 and. 87 of total fuel sales county wide by volume respec. tively Therefore on average for every liter of fuel com. busted on road and upwind of Pasadena in 2010 the follow. ing can be assumed,Lgas 0 87 Lfuel 1,Ldies 0 13 Lfuel 2. Figure 2a shows the chemical speciation pro,file and the compound specific SOA mass yields. Y 1SOA 1Hydrocarbon for a composite fuel,comprising 13 diesel fuel and 87 gasoline fuel by.
Fig 1 Measured AMS PMF factor concentrations normalized by volume based on detailed chemical speciation profiles see. CO enhancement 1CO is the ambient CO minus the estimated Tables S5 S6 and S8 of Gentner et al 2012 As shown in. background CO 105 ppb as functions of photochemical age see Fig 2a the 2010 composite fuel composition is dominated. Hayes et al 2013 for a detailed description of how this figure was by species with fewer than 12 carbon atoms with the largest. constructed A The evolution of OA 1CO vs photochemical age contributions coming from branched alkanes and single ring. for Pasadena during CalNex separated by day of the week Error aromatics Note that the percentages listed in the legend. bars indicate the standard errors Photochemical age is determined. of Fig 2a sum up to 90 which corresponds to the, using the method of Parrish et al 2007 Also shown are the analo. unprecedented level of mass closure Gentner et al 2012. gous plots for B OOA and C SV OOA D Evolution of the PMF. component concentrations normalized to 1CO vs photochemical obtained in characterizing gasoline and diesel fuel Gentner. age et al 2012 estimated the SOA mass yields for pure gasoline. and pure diesel fuel using a combination of measured SOA. mass yields derived from laboratory chamber experiments. 1CO is relatively constant i e no enhancement at 9 6 g and approximate SOA mass yields based on box modeling. HOA CIOA sm 3 ppmv CO 1 Note that the average Based on the level of oxidation effectively constrained by. OOA enhancement corresponds to an average OH expo experimental measurements the SOA mass yields reported. sure of 58 3 109 molec cm 3 s 0 45 days and that the by Gentner et al 2012 are expected to be representative. average POA 1CO value is very similar to the value of of the first several generations of photochemical oxida. 9 4 g POA sm 3 ppmv CO 1 assumed by both Bahreini tion The compound specific SOA mass yields reported. et al 2012 and Gentner et al 2012 by Gentner et al 2012 are given in Fig 2b and Fig 2c. In this study we are primarily interested in the fraction shows the product of the estimated yields and the weight. of OOA attributable to anthropogenic fossil activity Based percent by carbon of the individual species in liquid fuel. on the 14 C analysis presented in Zotter et al 2014 70 In contrast to the cumulative distribution shown in Fig 2a. of the SV OOA enhancement corresponds to the fraction of roughly 50 of the expected SOA mass is attributable to. OOA that is attributable to anthropogenic fossil fuel activity species with fewer than 12 carbons and 50 is attributable. Some anthropogenic SOA such as from cooking emissions to species with more than 12 carbons Note that single ring. will be nonfossil Therefore we note that at 0 45 days of pho aromatics are predicted to make the most significant con. tochemical processing 70 of the SV OOA enhancement is tribution to the SOA budget Fig 2c The analysis in the. equal to 25 9 g SV OOA sm 3 ppmv CO 1 Fig 1c present study implicitly assumes that the SOA yields from. where 9 g SV OOA sm 3 ppmv CO 1 is the propagated Gentner et al 2012 which were mostly determined based. uncertainty associated with the OOA and CO measurements on chamber experiments with individual compounds apply. to the complex L A atmosphere consistent with the limited. evidence available for complex precursor mixtures Odum. et al 1997 1996,Vehicular exhaust emissions include water CO CO2. NOx and partially combusted hydrocarbons as well as a. www atmos chem phys net 14 2383 2014 Atmos Chem Phys 14 2383 2397 2014. 2386 J J Ensberg et al Impact of vehicular emissions on SOA. GPOM and CO emitted per liter of combusted fuel is. Weight Percent by Carbon WtC,Cumulative Distribution. GPOM EFGPOM gas Lgas EFGPOM dies Ldies 7,straight alkane 7 6. CO EFCO gas Lgas EFCO dies Ldies 8,6 branched alkane 37 3 60.
Cycloalkanes single branch 5 7,Cycloalkanes multi branch 6 4. Bicycloalkanes 1 9 40 Substituting Eqs 1 and 2 into Eqs 7 and 8 and divid. Tricycloalkanes 0 7,2 Single Ring Aromatic 27 4, 20 ing gives the amount of GPOM that is emitted per unit of CO. Cumulative Distribution,0 mass emitted defined here as EFGPOM CO. 0 5 10 15 20 25,SOA Mass Yield,1 EFGPOM gas 0 87 EFGPOM diesel 0 13. EFCO gas 0 87 EFCO diesel 0 13,EFGPOM CO 0 039 0 019 g GPOM g CO 1 10.
0 Converting grams to micrograms and normalizing the numer. 0 5 10 15 20 25, ator and denominator by air volume at standard conditions. Cumulative Distribution,273 K and 1 atm Eq 10 can be written as. straight alkane 0 3 Cycloalkanes single branch 0,branched alkane 0 3 Cycloalkanes multi branch 0 3. EFGPOM CO 0 039 0 019 g GPOM sm 3 g CO sm 3 1 11,WtC x Yield. 0 28 Bicycloalkanes 0 1 SR Aromatic 2 7, The CO emission units g CO sm 3 in Eq 11 can be con.
Tricycloalkanes 0 1 PAHs 0 5,Cumulative Distribution. verted to ppmv CO by using the following conversion factor. which is applicable at 273 K and 1 atm,0 5 10 15 20 25. Carbon Number,EFGPOM CO 0 039 0 019 g GPOM sm 3, Fig 2 Distribution of mass by chemical class based on California g CO sm 3 1 1250 g CO sm 3 ppmv CO 1 12. fuel sale data comprising 13 diesel and 87 gasoline by volume. top panel Distribution of compound specific SOA mass yields EFGPOM CO 48 9 24 3 g GPOM sm 3 ppmv CO 1 13. middle panel Relative contributions of each group of species to. predicted SOA calculated as the yields multiplied by weight per We assume that EFGPOM CO given by Eq 13 is represen. cent by carbon in liquid fuel bottom panel Data are from Ta tative of the average vehicle fleet and that the 70 of the. bles S5 S6 and S8 of Gentner et al 2012 SV OOA concentrations that are comprised of fossil car. bon at the Pasadena ground site are attributable to vehic. ular emissions Bahreini et al 2012 Hayes et al 2013. Using EFGPOM CO and 70 of the SV OOA enhancement, large contribution from unburned fuel that escapes combus. 25 9 g OOA sm 3 ppmv CO 1 given in Fig 1b the, tion Gentner et al 2012 argue that unburned fuel in ex.
average aggregate SOA mass yield required to obtain mass. haust emissions is the dominant source of newly formed SOA. closure at the Pasadena ground site Yreq can be determined. attributable to vehicular activity Emission factors reported. as follows, by Gentner et al 2012 which are based on CalNex 2010. measurements at the Caldecott Tunnel in Oakland CA for 1SOA 25 9 g SOA sm 3 ppmv CO. CO and for noncombusted gas phase organic mass GPOM 1GPOM 48 9 24 3 g GPOM sm 3 ppmv CO 1. emitted in the exhaust of gasoline gas and diesel dies en 51 1 31 4 14. This required overall SOA mass yield is to be compared. EFCO gas 14 7 5 88 g CO Lgas 1 3 with the estimated yields reported in Gentner et al 2012. Fig 2 for pure gasoline fuel and pure diesel fuel which. EFCO dies 4 5 1 80 g CO Ldies 1 4 are 2 3 0 7 and 15 5 respectively Based on the es. EFGPOM gas 0 45 0 18 g GPOM Lgas 1 5 timated yields for pure liquid gasoline and diesel fuel the. predicted SOA mass yield for a fuel comprising 87 gaso. EFGPOM dies 1 01 0 40 g GPOM Ldies 1 6, line and 13 diesel is 5 5 Note that the required SOA. mass yield is a lower bound because it is based on the as. where the uncertainties are assumed to be 40 based on sumption that 100 of the GPOM reacts within 0 45 days. average values reported in Tables S5 and S6 of McDonald OH exposure 58 3 109 molec cm 3 s of being emit. et al 2013 Therefore the total amount of noncombusted ted As shown in Table 1 the fraction of hydrocarbon reacted. Atmos Chem Phys 14 2383 2397 2014 www atmos chem phys net 14 2383 2014. J J Ensberg et al Impact of vehicular emissions on SOA 2387. Table 1 Fraction of hydrocarbon reacted for an OH exposure of Req Yield Pred Yield. Req Yield 87 Gas,Pred Yield 87 Gas Req Yield Pred Yield. 58 3 109 molec cm 3 s at 298 K and 1 atm Hydrocarbons shown 3 1 4 0 9. are abundant in a typical mixture of liquid gasoline and diesel fuel. Fraction reacted 1 exp kOH OH t 2 5,Hydrocarbon Fraction OH reaction rate 1. Aggregate SOA Mass Yield,reacted constant,cm3 molec 1 s 1 0 8 0 5.
benzenea 0 069 1 22 10 12 0 6 0 4,toluenea 0 280 5 63 10 12. m xylenea 0 740 2 31 10 11 0 4,n hexaneb 0 272 5 45 10 12 0 2. n octaneb 0 398 8 71 10 12 0 5,n dodecaneb 0 555 1 39 10 11. a Reaction rate constants from Calvert et al 2002 0 0 0. 0 0 5 1 0 0 5 1 0 0 5 1,b Reaction rate constants from Atkinson 1997. Gasoline Fraction of Total Fuel Use by volume, Fig 3 Vehicular SOA mass yields compared to ambient SV OOA.
for an OH exposure of 58 3 109 molec cm 3 s is between mass yields assuming all fossil SV OOA is attributable to vehicular. 0 07 and 0 74 for several hydrocarbons abundant in gasoline emissions A Black line aggregate SOA mass yield required to. and diesel fuel To account for partial reaction of the emit match observations at the Pasadena ground site assuming all fossil. ted hydrocarbons we reduce each chemical constituent of SOA is attributable to vehicular emissions Green line SOA mass. the emitted GPOM Fig 2a by the fraction that would re yield of unburned fuel gasoline diesel components reported by. act after 0 45 days of photochemical aging The partially re Gentner et al 2012 Red line yield required for 87 gasoline and. acted EFGPOM CO Eq 13 is then determined by summing 13 diesel fuel state average Blue line SOA mass yield of liq. uid fuel for 87 gasoline and 13 diesel fuel state average Cyan. over all partially reacted GPOM components The total frac. line point at which the black line crosses the green line B Same. tion of GPOM reacted after 0 45 days of photochemical ag as A except EFGPOM gas have been increased by a factor of 2 35. ing ranges from 0 66 at 100 diesel to 0 43 at 100 gaso C Same as A except EFGPOM gas and EFGPOM dies have both. line and is 0 47 for fuel usage of 13 diesel and 87 been increased by a factor of 2 7 McDonald et al 2013 Error bars. gasoline by volume Reducing the EFGPOM CO by a fac correspond to propagated uncertainties and all plots have been ad. tor of 0 47 increases the required yield by a factor of 2 13 justed to account for partial reaction of hydrocarbons at 0 45 days of. Yreq 2 13 51 1 31 4 108 7 66 9 photochemical aging Required yields are based on SV OOA mea. The analysis thus far is based on the county specific fuel surements and 14 C measurements reported in Zotter et al 2014. usage of 13 diesel and 87 gasoline by volume How Hayes et al 2013 All quantities are plotted as functions of gaso. ever the dependence of the required overall SOA mass yield line and diesel fuel sales by volume. on any fractional fuel usage fgas fdies 1 is calculated as. EFGPOM CO fgas fdies Gentner et al 2012 as a function of fractional fuel usage. EFGPOM gas fgas EFGPOM dies fdies,which are calculated as. FR fgas fdies 15,EFCO gas fgas EFCO dies fdies Ypred. 25 9 g OOA sm 3 ppmv CO 1 Ygas EFGPOM gas fgas Ydies EFGPOM dies fdies. Yreq 16 17, EFGPOM CO fgas fdies EFGPOM gas fgas EFGPOM dies fdies. where FR fgas fdies is the fraction of GPOM reacted FR where Ygas 0 023 0 007 and Ydies 0 15 0 05 As. fraction reacted after 0 45 days of photochemical aging for shown in Fig 3a the required and predicted SOA yields. a given fractional fuel usage The predictions of Eq 16 are match if the fuel usage is 3 gasoline and 97 diesel and. shown in Fig 3a Note that as a result of gasoline having a the propagated error bars intersect when the fuel usage is. higher EFCO and a lower EFGPOM than its diesel counterpart 40 gasoline and 60 diesel both of which are far from. the required overall SOA mass yield increases as the frac the reported fuel usage of 87 gasoline and 13 diesel. tion of gasoline increases In other words the emission ratio For reference the closest any county in California comes to. EFGPOM EFCO decreases as the fraction of gasoline use in the required fuel usage is Glenn County northern Califor. creases thereby requiring a greater fraction of the emitted nia which had fuel sales that were 58 gasoline and 42. GPOM to be converted to SOA to match observations at the diesel. Pasadena ground site Also shown in Fig 3a are the SOA. mass yields predicted Ypred based on the values reported by. www atmos chem phys net 14 2383 2014 Atmos Chem Phys 14 2383 2397 2014. 2388 J J Ensberg et al Impact of vehicular emissions on SOA. Table 2 Measured fleet averaged fuel based CO and NMHC emission factors g kg 1 of fuel reported by Fujita et al 2012 Gentner et al. 2012 Numerical values in the right most column are calculated using the conversion factor 1250 g CO sm 3 ppmv CO 1. Date Temperature EFCO EFNMHC EFNMHC EFCO EFNMHC EFCO. values from Fujita et al 2012 F g CO g NMHC g NHMC g NMHC sm 3. kg fuel 1 kg fuel 1 g CO 1 ppmv CO 1,21 Aug Sat p m 95 23 0 1 59 0 069 86 3. 22 Aug Sun p m 92 25 4 1 98 0 078 97 5,24 Aug Tue a m 92 16 7 1 40 0 084 105.
24 Aug Tue p m 101 19 1 2 51 0 131 164,25 Aug Wed a m 92 18 9 1 35 0 071 88 8. 25 Aug Wed p m 102 30 4 3 05 0 100 125,28 Aug Sat a m 72 25 9 1 09 0 042 52 5. 29 Aug Sun a m 70 10 7 0 51 0 048 60 0,Mean 21 3 1 69 0 078 97 5. Median 21 1 1 50 0 075 93 8,Values from Gentner et al 2012 0 039 48 8. 3 2 Potential explanations plete combustion and evaporative emissions during stabilized. running conditions, We examine the sensitivity of the required composite SOA.
3 2 1 Emission factor uncertainty, mass yield by increasing the EFGPOM gas reported by Gen. tner et al 2012 by a factor of 2 35 which increases the. Given the discrepancy between predictions and observations total EFGPOM CO given by Eq 13 by a factor of 2 in. of aggregate SOA mass yields shown in Fig 3a one deduces creasing EFGPOM CO from 48 9 to 98 3 g GPOM sm3 ppmv. that for SOA predictions and observations to match i e for CO 1 at 87 gasoline and 13 diesel to match the mean. the black and green lines in Fig 3a to cross at fgas 0 87 value reported by Fujita et al 2012 Fig 3b As shown. 1 the predicted aggregate SOA mass yield green line must in Fig 3b increasing EFGPOM gas by a factor of 2 35 re. be higher or 2 the required SOA mass yield black line duces the required SOA mass yields However this also re. must be lower or both 1 and 2 are true One way by duces the predicted yields since the SOA yield from pure. which the required composite SOA mass yield decreases is gasoline is lower and since the gasoline terms in Eq 17. via an overall increase in the ratio of EFGPOM EFCO ei have a larger impact than the diesel terms The net result. ther by reducing EFCO and or increasing EFGPOM To as is that the required and predicted yields still match if the. sess the accuracy of the emission factors reported in Gen fuel usage is 3 gasoline and 97 diesel and the propa. tner et al 2012 we consider those reported in Fujita et al gated error bars still intersect when the fuel usage is 40. 2012 given in Table 2 During August 2010 Fujita et al gasoline and 60 diesel Note that if the EFGPOM gas were. 2012 measured emission factors for CO and total products increased even further the predicted yield Eq 17 would. of incomplete combustion noncombusted hydrocarbons asymptotically approach Ygas and the required yield would. evaporative emissions nonmethane hydrocarbons NMHC approach zero Eq 16 In this analysis we have assumed. obtained from tunnel measurements in Van Nuys California the evaporative emissions and products of incomplete com. which is 32 km west of the Pasadena ground site Based on bustion have the same SOA mass yield as the tail pipe ex. the results presented in Fujita et al 2012 Table 2 emis haust emissions However evaporative emissions will be en. sion ratios measured in the Van Nuys tunnel range from 52 5 riched in small alkanes under ambient conditions According. to 164 g NMHC sm 3 ppmvCO 1 with an average value to Fig 2 of Gentner et al 2012 the SOA mass yield of. of 97 5 g NMHC sm 3 ppmvCO 1 Similarly to Gentner evaporative emissions is expected to be lower than tail pipe. et al 2012 Fujita et al 2012 derived these fleet average emissions by a factor of 10 Therefore this analysis repre. emission factors from vehicles traveling through a tunnel at sents a conservative upper limit since evaporative emissions. near constant speeds of approximately 40 mph and excluded are not expected to contribute substantially to the SOA bud. cold start emissions idle emissions and diurnal and hot get The SOA formation potential of products of incomplete. soak evaporative hydrocarbon emissions The Gentner et al combustion and incomplete catalytic converter oxidation are. 2012 value is consistent with the lower end of the values examined more thoroughly in Sect 3 2 4. reported in Fujita et al 2012 The spread of values reported McDonald et al 2013 recently assessed long term trends. by Fujita et al 2012 is most likely attributable to the fact 1990 2010 in EFGPOM CO emission ratios for several US. that the emission factors derived include products of incom. Atmos Chem Phys 14 2383 2397 2014 www atmos chem phys net 14 2383 2014. J J Ensberg et al Impact of vehicular emissions on SOA 2389. Table 3 Gasoline vehicle specific emission ratios EFNMHC EFCO predicted by EMFAC2011 http www arb ca gov emfac for the South. Coast Air Basin in summer 2010 Emission ratios are based on daily CO and NMHC emission rates calculated by EMFAC2011 Emission. ratios include all drive cycle components i e running idle start diurnal evaporative hot soak evaporative running evaporative and resting. evaporative Rows are ordered in descending population Numerical values in g NMHC m 3 ppmv CO 1 columns are calculated using. the conversion factor 1250 g CO sm 3 ppmv CO 1 Note that the values predicted by EMFAC are higher than what is reported by Gentner. et al 2012 because they include products of incomplete combustion evaporative emissions and start emissions. Vehicle Class g NHMC g NMHC sm 3 Population,g CO 1 ppmv CO 1. Values from 0 031 38 3 Caldecott,Gentner et al 2012 Tunnel. LDA 0 116 145 5 566 383,LDT2 0 093 116 1 806 334,MDV 0 081 101 1 474 925. LDT1 0 112 140 655 343,LHD1 0 115 144 257 882,MCY 0 161 201 213 296.
MH 0 035 43 8 58 258,LHD2 0 112 140 27 933,T6TS 0 096 120 22 177. OBUS 0 088 110 7278,UBUS 0 100 125 1766,T7IS 0 051 63 8 1501. SBUS 0 068 85 0 1491, See http www arb ca gov msei emfac2011 pl users guide 122112 pdf for a detailed. description of each vehicle class, urban areas As shown in Fig 3b of McDonald et al 2013 tive emissions diurnal evaporative emissions etc that were. owing to differences in driving conditions and engine loads not the focus of the analysis by Gentner et al 2012 but are. the EFGPOM CO emission ratios derived from tunnel measure assessed more closely in this study. ments such as those of Gentner et al 2012 and Fujita et al. 2012 may be lower than those derived from on road studies 3 2 2 Emission ratios from other drive cycle phases. in Los Angeles by a factor of 2 7 Therefore to determine. the upper limit of EFGPOM CO that should be used in this By sampling emissions within urban tunnels for sufficient. analysis we increase the overall gas diesel EFGPOM CO periods of time Fujita et al 2012 and Gentner et al. Eq 13 by a factor of 2 7 Doing so reduces the required 2012 estimated average emission factors However nei. yield Eq 14 by a factor of 0 37 Yreq 0 37 108 7 ther study included emissions from drive cycle phases other. 40 2 As shown in Fig 3c when the overall EFGPOM CO is than stabilized running in the emission factors used in. increased by a factor of 2 7 the predicted and required yields this study To estimate the impact of drive cycle phase on. match if the fuel usage is 35 gasoline and 65 diesel emission factor ratio we use the California EMission FACtor. and the propagated uncertainties intersect if the fuel usage model EMFAC2011 http www arb ca gov emfac com. is 65 gasoline and 35 diesel bined with summer 2010 data for the South Coast Air Basin. Given the lack of agreement between predicted and re SoCAB of California Emission factors are weighted and. quired SOA mass yields Fig 3 when using the emission aggregated by vehicle year populations and speed distribu. ratios from Fujita et al 2012 Gentner et al 2012 and tions and include all drive cycle components i e running. McDonald et al 2013 if the SV OOA 1CO enhancements idle start diurnal evaporative hot soak evaporative running. shown in Fig 1c are primarily attributable to vehicular emis evaporative and resting evaporative Emission factor ratios. sions at least one of the following must be true 1 vehicu based on daily average emission rates for all EMFAC2011. lar emission rates of gas phase organic mass relative to CO gasoline and diesel vehicle types are given in Tables 3 and. are substantially larger than those recently measured or 2 4 respectively As shown in Table 3 EMFAC2011 predicts. the SOA mass yields of pure gasoline and pure diesel ex gasoline emission factor ratios that are generally consistent. haust are substantially i e a factor of 3 16 higher than with the values reported by Fujita et al 2012 and are. what has been measured previously In the next section we 2 3 5 times higher than the value reported by Gentner et al. explore possibility 1 in the context of drive cycle phases 2012 Based on the results shown in Fig 3b increasing. e g cold start emissions idle emissions hot soak evapora the gasoline emission factor ratio by 2 5 reduces both the. www atmos chem phys net 14 2383 2014 Atmos Chem Phys 14 2383 2397 2014. 2390 J J Ensberg et al Impact of vehicular emissions on SOA. predicted and required SOA mass yields which does not im A. Concentration CO Gas or Particle g sm 3 ppmv 1, prove agreement As shown in Table 4 the diesel emission SingleRingAromatic.
C C C Alkanes, factor ratios predicted by EMFAC2011 are very similar to the 6 9 11. Arom C6 C9 C11 Alkanes, value reported by Gentner et al 2012 These results show 50. that the required and predicted yields do not match even if. all drive cycle phases are accounted for Therefore one con 40 Slope 62. cludes that either the SOA mass yields for gasoline and diesel. exhaust are significantly higher than what has been previ 30 Slope 57. ously reported or nonvehicular source categories contribute Slope 51. significantly to the anthropogenic fossil OOA budget mea. sured at the Pasadena ground site Both of these possibilities. are explored in the next section,3 2 3 Ambient NMHC 1CO ratios. 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8, The analysis up to this point has been based on measured and. Photochemical age days, predicted NMHC CO vehicular emission ratios and mea.
sured ambient OOA 1CO ratios at the Pasadena ground Fig 4 Measured PMF OOA factor concentrations normalized by. site This analysis is now extended to include all upwind CO enhancement 1CO is the ambient CO minus the estimated. NMHC source categories vehicular and nonvehicular by background CO 105 ppb as functions of photochemical age Also. comparing measured ambient NMHC 1CO ratios to mea shown are lumped gas phase VOC concentrations normalized by. sured ambient OOA 1CO at the Pasadena ground site The 1CO See Table 6 for the chemical speciation of each lumped. four main source categories of NMHC in southern Califor species. nia not including trans Pacific transport which is thought. to be unimportant for SOA formation in the L A Basin. due to long transport times and intense dilution are sta sistent with vehicular exhaust being the dominant source of. tionary area wide mobile and natural nonfossil Based on these compounds Furthermore in contrast to the numbers. the 2009 Almanac Emission Projection Data reported by the given in Table 5 Borbon et al 2013 found that emissions. CARB http www arb ca gov app emsinv emssumcat php from gasoline powered vehicles dominated the urban anthro. the 2010 annual emissions of reactive organic gas ROG and pogenic NMHC budget during CalNex. CO from each source are given in Table 5 Note that CARB One particularly interesting feature of Fig 4 is that even if. reports ROG emission rates which are similar to NMHC all upwind sources of linear alkanes C6 C9 C11 and single. but do not include several low reactive organic compounds ring aromatics are accounted for the required aggregate SOA. such as ethane acetone CFCs and HCFCs As shown in mass yield is still 92 92 OOA 1CO slope divided. Table 5 on road motor vehicles are reported to contribute by negative NMHC 1CO slope 57 62 This required. 27 29 of all ROG emissions in the South Coast Air yield may be overestimated because only light straight chain. Basin and Los Angeles County Mobile sources other than C6 C9 C11 alkane and single ring aromatic C12 con. on road vehicles e g aircraft trains ocean going vessels centration measurements are available whereas the major. and off road equipment such as forklifts are reported to con ity of alkanes in the ambient are expected to be branched. tribute 21 of the ROG emissions Fig 2c That being said the required yield of 92 is still. Figure 4 shows two lumped NMHC concentrations e g inexplicably large considering that the single ring aromatic. single ring aromatics and small alkanes normalized by component of vehicular exhaust is expected to produce 2 5. 1CO as functions of photochemical age See Table 6 for a times more SOA than the alkane component Fig 2c A. list of all compounds included in Fig 4 As shown in Fig 4 similar correspondence between the magnitude of aromatic. similarly to the roughly linear increases in OOA 1CO with hydrocarbon decreases and SOA increases was observed by. increasing photochemical age gas phase alkane C6 C9 de Gouw et al 2005 in the 2002 New England Air Qual. C11 and single ring aromatic concentrations both exhibit ity Study It is possible that alkanes and aromatics with 12. roughly linear decreases with increasing photochemical age or more carbon atoms are contributing to the SOA bud. Note that adding the normalized alkanes and single ring aro get However alkanes and aromatics C12 attributable to. matic concentrations at zero photochemical age suggests an vehicular activity are abundant only in diesel exhaust and. emission ratio of 55 g GPOM sm 3 ppmv CO 1 which not in gasoline exhaust If alkanes C12 were contribut. is similar to the estimated emission ratio given by Eq 13 ing substantially to the L A SOA budget one would expect. Although this is not proof the linear decrease in normal to see a significant decrease in OOA concentrations on the. ized NMHC concentrations with photochemical age and the weekends when diesel activity is reduced by 50 How. similarity between estimated emission ratios are both con ever this possibility is not supported by the conclusions of. Atmos Chem Phys 14 2383 2397 2014 www atmos chem phys net 14 2383 2014. J J Ensberg et al Impact of vehicular emissions on SOA 2391. Table 4 Diesel vehicle specific emission ratios EFNMHC EFCO predicted by EMFAC2011 http www arb ca gov emfac for the South. Coast Air Basin in summer 2010 Emission ratios are based on daily CO and NMHC emission rates calculated by EMFAC2011 Emission. ratios include all drive cycle components i e running idle start diurnal evaporative hot soak evaporative running evaporative and resting. evaporative Rows are ordered in descending population Numerical values in g NMHC m 3 ppmv CO 1 columns are calculated using. the conversion factor 1250 g CO sm 3 ppmv CO 1,Vehicle Class g NHMC g NMHC m 3 Population. g CO 1 ppmv CO 1, Values from Gentner et al 2012 0 224 280 0 Caldecott Tunnel. LHD1 0 204 255 80 690,T6 instate small 0 256 320 37 131. LHD2 0 203 254 27 901,LDA 0 225 281 19 184,T6 instate heavy 0 275 344 15 303. T7 tractor 0 219 274 11 037,MH 0 261 326 10 110,T7 POLA 0 198 248 9818.
T7 Single 0 220 275 8951,UBUS 0 217 271 7084,T6 instate construction small 0 256 320 5410. T7 NNOOS 0 224 280 5372,T7 CAIRP 0 227 284 5325,T6 Public 0 272 340 5282. T7 SWCV 0 232 290 4839,SBUS 0 314 393 4388,T7 Public 0 267 334 3579. All Other Buses 0 278 348 3178,T7 single construction 0 220 275 3176. T7 tractor construction 0 221 276 2306,T6 instate construction heavy 0 275 344 2242.
T7 NOOS 0 231 289 1939,MDV 0 205 256 1504,Motor coach 0 232 290 1313. LDT1 0 236 295 953,T6 utility 0 238 298 890,LDT2 0 245 306 861. T7 utility 0 243 304 423,T7 CAIRP construction 0 227 284 392. T7 Ag 0 217 271 231,T6 Ag 0 291 364 187,T6 CAIRP small 0 244 305 136. T6 OOS small 0 244 305 78,T6 CAIRP heavy 0 258 323 44.
T6 OOS heavy 0 258 323 25, See http www arb ca gov msei emfac2011 pl users guide 122112 pdf for a detailed description of each vehicle. Hayes et al 2013 and Bahreini et al 2012 or the emis that products of incomplete combustion and products of in. sion ratio analysis presented in this study complete catalytic converter oxidation may be efficient SOA. precursors Specifically Gordon et al 2013 used a labora. 3 2 4 Incomplete combustion catalytic converter tory chamber to investigate SOA formation from photooxi. oxidation products dation of tail pipe emissions from 15 light duty gasoline ve. hicles LDGVs spanning a wide range of types model years. The analysis presented thus far is based on the assump and emission standards The 15 LDGVs are grouped accord. tion that unburned fuel in exhaust emissions is the dominant ing to model year into three vehicle classes termed preLEV. source of newly formed SOA attributable to vehicular ac LDGVs manufactured prior to 1995 LEV1 LDGVs man. tivity Gentner et al 2012 However recent work suggests ufactured between 1995 and 2003 and LEV2 LDGVs. www atmos chem phys net 14 2383 2014 Atmos Chem Phys 14 2383 2397 2014. 2392 J J Ensberg et al Impact of vehicular emissions on SOA. Table 5 CARB 2010 estimated daily emission rates annual average Units are in metric tons per day. Source Los Angeles County South Coast Air Basin,CO ROG CO ROG. Stationary sources,Fuel combustion 24 1 1 3 4 3 1 1 34 1 1 1 5 8 0 9. Waste disposal 0 8 0 0 9 0 2 1 1 0 9 1 1 4, Cleaning and surface coatings 0 0 0 25 8 6 6 0 1 0 40 7 6 1. Petroleum production and marketing 8 9 0 5 25 1 6 4 8 9 0 3 33 2 5 0. Industrial processes 1 3 0 11 6 3 0 2 5 0 20 2 3 0. Total stationary sources 35 0 1 9 67 7 17 3 46 8 1 5 109 0 16 5. Area wide sources,Solvent evaporation 0 0 82 7 21 2 0 0 129 4 19 5.
Miscellaneous processes 51 2 2 8 5 4 1 4 112 3 3 6 14 7 2 2. Total area wide sources 51 2 2 8 88 0 22 5 112 3 3 6 144 1 21 8. Mobile sources, On road motor vehicles 1096 3 60 0 113 1 29 0 1817 6 58 4 182 8 27 6. Other mobile sources 579 5 31 7 81 0 20 7 973 2 31 3 140 1 21 1. Total mobile sources 1675 8 91 7 194 1 49 7 2790 8 89 6 322 9 48 7. Natural nonanthropogenic sources, Natural sources 65 0 3 6 40 5 10 4 164 2 5 3 86 5 13 1. Total natural sources 65 0 3 6 40 5 10 4 164 2 5 3 86 5 13 1. http www arb ca gov app emsinv emssumcat php, CARB reports ROG emission rates which are similar to NMHC but do not include several low reactive organic compounds such as ethane acetone. CFCs and HCFCs, Table 6 Chemical constituents of lumped species shown in Fig 4 SOA. for each chamber experiment Yveh class These quantities in. clude products of incomplete combustion and catalytic con. Alkanes C6 C9 C11 Single ring aromatics version and are given in Table 7 for reference. n hexane benzene, We first calculate a fleet average LDGV NMOG emission.
n nonane toluene factor based on the values reported by Gordon et al 2013. n decane o xylene see Table 7,n undecane m xylene,p xylene EFfleet. NMOG Fleet Fraction preLEV EFNMOG,1 ethyl benzene,Fleet Fraction LEV1 EFLEV1. isopropyl benzene Fleet Fraction LEV2 EFLEV2,n propyl benzene. 1 ethyl 2 methyl benzene EFfleet,NMOG 0 07 4 5 g NMOG Lgas 1. 1 ethyl 3 methyl benzene 0 36 1 3 g NMOG Lgas 1,1 ethyl 4 methyl benzene.
1 2 3 trimethylbenzene 0 57 0 4 g NMOG Lgas 1 19,1 2 4 trimethylbenzene EFfleet. NMOG 1 01 g NMOG Lgas 1,1 3 5 trimethylbenzene, The total NMOG emission factor for the LDGV fleet re. ported by Gordon et al 2013 Eq 20 is similar to the value. manufactured 2004 or later For each vehicle class Gordon reported in McDonald et al 2013 and is roughly a factor of. et al 2013 report median emission factors for CO median 2 higher than that reported by Gentner et al 2012 These. emission factors for all nonmethane organic gases NMOG differences in emission factors are most likely attributable to. median emission factors for speciated and nonspeciated or the differences in LDGV driving conditions in each study. ganic gases that are expected to be SOA precursors and ag In a similar manner we calculate a fleet average LDGV. gregate SOA mass yields required to obtain mass closure CO emission factor based on the values reported by Gordon. Atmos Chem Phys 14 2383 2397 2014 www atmos chem phys net 14 2383 2014. J J Ensberg et al Impact of vehicular emissions on SOA 2393. Table 7 Median emission factors and SOA mass yields reported in Gordon et al 2013 These values include products of incomplete. combustion and products of incomplete catalytic converter oxidation. preLEV LEV1 LEV2,Median EFCO gCO Lgas 1 210 25 9,Median EFNMOG gNMOG Lgas 1 4 5 1 3 0 40. LDGV fleet fraction 0 07 0 36 0 57, Effective SOA mass yield g g 1 0 008 0 03 0 17 0 07 0 25. 0 008 0 10 0 16, Values in parentheses are the arithmetic mean of the reported SOA mass yield range.
et al 2013 see Table 7 The SOA mass yield given in Eq 28 is 4 times larger than. the yield for pure gasoline reported by Gentner et al 2012. CO 21 6 g CO Lgas 21 Ygas 2 3 With respect to diesel fueled vehicle emis. sions Jathar et al 2013 showed that unburned diesel fuel. The fleet average CO emission factor given by Eq 21 is and combustion tail pipe exhaust from diesel fueled vehicles. 50 larger than the value reported by Gentner et al 2012 have similar SOA formation potentials As shown in Fig 4. Eq 3 of Jathar et al 2013 the experimentally derived aggregate. To facilitate a consistent comparison with the analysis pre SOA mass yields for diesel exhaust are very similar to the. sented in Gentner et al 2012 the SOA mass yields pre value reported by Gentner et al 2012 Ydies 15 which. sented in Gordon et al 2013 have been rescaled based on suggests that this value is representative of diesel fueled ve. the total NMOG tail pipe emissions and not the fraction of hicles in California However in this analysis we reduce the. NMOG emissions that is expected to be comprised of SOA EFNMOG dies to 0 69 g NMOG L dies 1 to account for. precursors Prec Therefore the SOA mass yields reported the fraction of nondiesel particulate filter equipped heavy. in Table 7 are roughly half as large as those reported in Fig 7 duty diesel vehicles in the South Coast Air Basin based on. of Gordon et al 2013 discussions in May et al 2014. To determine the impact of partial combustion and incom. YpreLEV 2 0 38 g SOA Prec g NMOG 0 8 22, plete catalytic conversion on ambient SOA formation the. YLEV1 6 33 0 51 g SOA Prec g NMOG analysis presented in Fig 3a has been redone using the exper. 10 3 17 2 23 imentally derived LDGV EFNMOG EFCO and the SOA mass. YLEV2 15 50 0 49 g SOA Prec g NMOG yield given in Eqs 20 21 and 28 respectively see Fig 5a. As shown in Fig 5a using the values reported by Gordon. 16 7 25 2 24, et al 2013 produces results that are qualitatively identical. where the SOA Prec NMOG conversion factors are taken to those shown in Fig 3 As discussed in the next paragraph. directly from Fig 3 of Gordon et al 2013 Using these val the impact of predicted yield uncertainty is demonstrated via. ues a fleet average SOA emission factor can also be approx sensitivity analyses Therefore the predicted yield error bars. imated are excluded from Fig 5a, To account for the uncertainty associated with the SOA. preLEV yield scaling technique used above and to determine the up. SOA Fleet Fraction preLEV Y, per limit of the SOA formation potential of gasoline vehicles. Fleet Fraction LEV1 Y SOALEV1 EFLEV1, NMOG we have conducted similar analyses assuming Ygas 16.
Fleet Fraction LEV2 Y SOALEV2 EFLEV2, NMOG and Ygas 25 which are the upper limits of the LEV1 and. 25 LEV2 vehicle classes respectively reported by Gordon et al. 2013 As shown in Fig S1 although increasing Ygas to its. SOA 0 07 4 5 0 008 g NMOG Lgas, upper limit does improve agreement to some extent the pre. 0 36 1 3 0 10 g NMOG Lgas 1 dicted and required yields still differ by more than a factor. 0 57 0 4 0 16 g NMOG Lgas 1 26 of 3 even when using the highest yields reported by Gordon. et al 2013 To account for the uncertainty associated with. Dividing Eq 26 by Eq 20 gives an approximate experi calculating the fraction of emitted SOA precursors that have. mentally derived fleet averaged SOA mass yield undergone a chemical reaction after 0 45 days of photochem. ical aging an additional sensitivity analysis was conducted. Y SOALDGV fleet EFfleet fleet, SOA EFNMOG 100 27 in which 100 of the emitted NMOG is assumed to have. Y SOALDGV fleet, 9 28 reacted see Fig S2 As shown in Fig S2 assuming 100. www atmos chem phys net 14 2383 2014 Atmos Chem Phys 14 2383 2397 2014. 2394 J J Ensberg et al Impact of vehicular emissions on SOA. Req Yield Pred Yield Req Yield 87 Gas,A Ydies 15 Ygas 9.
Pred Yield 87 Gas,Req Yield Pred Yield, larger than the fleet average SOA 1CO enhancement slope. 70 SVOOA CalNex 8 g m 3 ppmvCO 1 day 1 and 3 5 times larger than. pre LEV SOA before 1995, LEV1 SOA 1995 2003 the LEV2 vehicle class slope Note that the results presented. LEV2 SOA after 2003, Fleet Average SOA in Fig 5b are self consistent and therefore are not influenced. 1 4 35 by the uncertainty associated with the emission factors and. aggregate SOA mass yields reported by Gordon et al 2013. Concentration CO SOA or SVOOA g sm,1 2 30 Slope 57. Aggregate SOA Mass Yield, and Gentner et al 2012 but they are susceptible to other.
factors For instance Gordon et al 2013 do not account for. loss of organic vapors directly to chamber walls Matsunaga. and Ziemann 2010 Although highly uncertain as acknowl. edged by Gordon et al 2013 accounting for vapor phase. Slope 16 wall loss would increase their estimated SOA production. Slope 8 To our knowledge there is currently no combination. of published vehicular emission factors and SOA mass. 0 0 2 0 4 0 6 0 8 1,0 0 1 0 2 0 3 0 4 0 5, yields derived from laboratory experiments or measured. Gasoline Fraction of Total Fuel Use by volume Photochemical age days. SOA 1CO enhancements based on tail pipe exhaust emis. Fig 5 Same as Fig 3 except emission factors for gasoline fueled. sions that can explain the measurements presented in Fig 1. vehicles and aggregate SOA mass yields are based on the experi Based on the analysis presented in this section a robust con. mentally derived values reported in Gordon et al 2013 A Ag clusion is that either the SOA mass yields for vehicular tail. gregate SOA mass yield for gasoline exhaust is 9 which is con pipe exhaust are significantly higher than what has been re. sidered representative of the California LDGV fleet B Measured cently reported or nonvehicular source categories contribute. PMF SV OOA factor concentrations normalized by CO enhance significantly to the anthropogenic fossil OOA budget mea. ment 1CO is the ambient CO minus the estimated background CO sured at the Pasadena ground site For the latter possibility to. 105 ppb as functions of photochemical age Also shown are exper be true the nonvehicular fossil emissions must be comprised. imentally derived SOA 1CO enhancements resulting from pho of compounds other than those listed in Table 6. tooxidation of tail pipe emissions from 15 LDGVs recruited from. the California in use fleet All LDGV experiments were conducted 3 2 5 Off road vehicular emissions. in a portable chamber under urban like conditions and all LDGV. data are taken directly from Gordon et al 2013 A large part of this analysis is based on on road gaso. line diesel fuel sales and accounting for off road use of. diesel may increase the fraction of total diesel fuel use by. conversion of NMOG effectively reduces the required SOA several percentage points However this is not expected to. mass yields by a factor of 2 The predicted yields shown in influence our conclusions because as shown in Figs 5 S1. Fig S2c are still lower than the required yields by a factor of and S2 significant discrepancies exist at virtually all gaso. 1 7 We emphasize that there is a significant lack of closure line diesel fuel usage ratios In addition looking at the to. between expected and observed organic aerosol concentra tal mobile sources category in Table 5 which represents. tions attributable to fossil fuel emissions even when assum the sum of all on road and off road mobile emissions we. ing 100 NMOG conversion and an LDGV fleet averaged calculate the emission factor ratio for L A and SoCAB. SOA mass yield of 25 Both assumptions are expected to both to be 145 g ROG m 3 ppmvCO 1 still using the. be very unrepresentative of ambient conditions in California 1250 g CO sm 3 ppmv CO 1 conversion factor Assum. A more straightforward way to assess the impact of ing that 50 of the ROG has reacted after 0 45 days. partial combustion and incomplete catalytic conversion on of photochemical aging and that the aggregate SOA mass. SOA formation from gasoline exhaust is to compare the yield is 10 we calculate an SOA enhancement ratio of. SOA 1CO enhancement ratios measured by Gordon et al 7 25 g SOA m 3 ppmvCO 1 This value is well below the. 2013 directly to the SV OOA 1CO enhancement ra 25 g SV OOA m 3 ppmvCO 1 measured during CalNex. tios measured at the Pasadena ground site during the Cal Fig 1 Although this result is consistent with the other re. Nex field campaign see Fig 5b As shown in Fig 5b sults presented in this study there is considerable uncertainty. the SOA 1CO enhancements for all three LDGV vehi associated with this calculation and future work should fo. cle classes are lower than the CalNex measured value at cus on obtaining detailed speciation profiles and expected. 0 14 days of photochemical aging Average SOA 1CO SOA mass yields for all major anthropogenic ROG sources. enhancement slopes g m 3 ppmvCO 1 day 1 are cal in southern California. culated for each vehicle class by extending a straight. line from the origin through the measured data points. As shown in Fig 5b the average SV OOA 1CO en, hancement slope 57 g m 3 ppmvCO 1 day 1 is 7 times. Atmos Chem Phys 14 2383 2397 2014 www atmos chem phys net 14 2383 2014. J J Ensberg et al Impact of vehicular emissions on SOA 2395. 4 Conclusions Acknowledgements The authors would like to thank R Bahreini. D Gentner A Chan A Goldstein and two anonymous reviewers. Using the best available laboratory derived SOA mass yields for providing valuable comments This study was supported. the SV OOA 1CO enhancements attributable to anthro by NOAA Climate Program Office s AC4 program award no. pogenic fossil activity Fig 1 cannot be explained by the NA13OAR4310058 P L Hayes and J L Jimenez thank CARB. measured and predicted NMOG CO vehicular emission ra 08 309 and 11 305 DOE BER ASR DE SC0006035 and a. tios or the measured ambient NMHC 1CO ratios This con CIRES Visiting Fellowship. clusion is based on the following observations,Edited by S A Nizkorodov. Emission factors and estimated yields reported in Gen. tner et al 2012 Fujita et al 2012 McDonald, et al 2013 and calculated using EMFAC2011 signif References. icantly underpredict OOA 1CO enhancements when, compared to CalNex observations Aiken A C DeCarlo P F Kroll J H Worsnop D R Huff.
man J A Docherty K S Ulbrich I M Mohr C Kimmel, Accounting for emissions from all drive cycle phases. J R Sueper D Sun Y Zhang Q Trimborn A Northway, e g start idle evaporative running etc does not M Ziemann P J Canagaratna M R Onasch T B Alfarra. improve agreement between predicted and required M R Prevot A S H Dommen J Duplissy J Metzger A. SOA mass yields significantly Baltensperger U and Jimenez J L O C and OM OC ra. tios of primary secondary and ambient organic aerosols with. Accounting for all upwind sources of single ring aro high resolution time of flight aerosol mass spectrometry Envi. matics and light alkanes C6 C9 C11 does not im ron Sci Technol 42 4478 4485 2008. prove agreement between predicted and required SOA Allan J D Williams P I Morgan W T Martin C L Flynn M. mass yields significantly J Lee J Nemitz E Phillips G J Gallagher M W and Coe. H Contributions from transport solid fuel burning and cook. Accounting for products of incomplete combustion ing to primary organic aerosols in two UK cities Atmos Chem. and products of incomplete catalytic converter oxida Phys 10 647 668 doi 10 5194 acp 10 647 2010 2010. tion does not improve agreement between predicted Atkinson R J Gas Phase Tropospheric Chemistry of Volatile Or. and required SOA mass yields significantly ganic Compounds 1 Alkanes and Alkenes Phys Chem Ref. Data 26 215 290 1997, With respect to the applicability of these results to other ma Bahreini R Middlebrook A M de Gouw J A Warneke C. jor urban areas ratios of OOA 1CO for Mexico City and Trainer M Brock C A Stark H Brown S S Dube W P. the northeastern US are similar or smaller by about a fac Gilman J B Hall K Holloway J S Kuster W C Perring. tor of 2 than those observed in L A as reported by Hayes A E Prevot A S H Schwarz J P Spackman J R Szi. et al 2013 Ratios of NMHC 1CO for emissions in the dat S Wagner N L Weber R J Zotter P and Parrish D. northeastern United States are very similar to those in the D Gasoline emissions dominate over diesel in formation of sec. L A area Borbon et al 2013 while those in Mexico City ondary organic aerosol mass Geophys Res Lett 39 L06805. doi 10 1029 2011GL050718 2012, are higher by about a factor of 2 Bon et al 2011 There. Bon D M Ulbrich I M de Gouw J A Warneke C Kuster, fore similar qualitative discrepancies between predicted and.
W C Alexander M L Baker A Beyersdorf A J Blake D, required yields albeit of somewhat lower magnitude may Fall R Jimenez J L Herndon S C Huey L G Knighton. exist in these urban areas as well W B Ortega J Springston S and Vargas O Measurements. We return to the question is it more likely that 1 am of volatile organic compounds at a suburban ground site T1. bient SOA mass yields are substantially larger than what in Mexico City during the MILAGRO 2006 campaign mea. has been derived experimentally or 2 vehicular emissions surement comparison emission ratios and source attribution. do not dominate SOA concentrations attributable to anthro Atmos Chem Phys 11 2399 2421 doi 10 5194 acp 11 2399. pogenic fossil activity in southern California Neither possi 2011 2011. bility can be categorically ruled out therefore both options Borbon A Gilman J B Kuster W C Grand N Chevaillier S. should be explored further particularly since their implica Colomb A Dolgorouky C Gros V Lopez M Sarda Esteve. R Holloway J S Stutz J Petetin H McKeen S Beekmann. tions for SOA control strategies are markedly different. M Warneke C Parrish D D and de Gouw J A Emission, ratios of anthropogenic volatile organic compounds in northern. mid latitude megacities Observations versus emission invento. Supplementary material related to this article is, ries in Los Angeles and Paris J Geophys Res Atmos 118. available online at http www atmos chem phys net 14 2041 2057 2013. 2383 2014 acp 14 2383 2014 supplement pdf California Air Resources Board Motor Vehicle Emission Fac. tor Emission Inventory Model EMFAC 2011 available at http. www arb ca gov msei msei htm last access 20 June 2013. www atmos chem phys net 14 2383 2014 Atmos Chem Phys 14 2383 2397 2014. 2396 J J Ensberg et al Impact of vehicular emissions on SOA. 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