Characterization of Organic Aerosol Formation and Processing in California from Airborne Measurements R. Bahreini, A.M. Middlebrook, C. Warneke, J. de Gouw, J. Holloway, S. Brown, A. Neuman, J.M. Roberts, A. Perring, J. Schwarz, R. Spackman, C.A. Brock, M.T. Trainer, T.B. Ryerson, D.D. Parrish CalNex Data Workshop May 19, 2011 Picture by H. Stark

Introduction CalNex-2010:  April 30- June 22  NOAA WP-3D, based in Ontario  Day/night, Weekend/weekday flights in LA  San Joaquin and Sacramento Valley flights  Mix of local sources Outline  Emphasis on LA flights 6 day flights; 4 night flights OA formation and processing (in BL) Weekend vs. weekday OA Predictability of SOA using measured VOCs and known SOA yields

AMS Quantification- LA flights Sum of AMS and BC mass well correlated with mass estimated from size distributions

OA vs. CO- LA flights, Altitude < 1500 m Sampled air masses have OA/CO greater than previously estimated primary ratio (de Gouw et al., JGR, 2008)

OA Processing- Daytime, <1500 m Downtown LA Redlands Long Beach Daytime, Fresh: NO x /(NO x +HNO 3 +PAN) > 0.8 Daytime, Aged : NO x /(NO x +HNO 3 +PAN) < 0.3 SOA production during aging (2-3 days) increases OA/CO by factor of ~2 de Gouw et al., 2008, Warneke et al., 2007 Toluene/Benzene=3.7 [OH]=2e6 molec./cm 3

OA Processing- Nighttime, < 500 m Nighttime, Fresh: NO x /(NO x +HNO 3 +PAN+2*N 2 O 5 +NO 3 ) > 0.8 OA/CO in nighttime-fresh BL comparable to daytime-fresh air Downtown LA Redlands Long Beach

OA Processing- Oxygenated OA Increase in OA/CO brings along increase in fraction of oxygenated species Downtown LA Redlands Long Beach m 44 : fragment from highly oxygenated OA f 44 =m 44 /OA

OA Processing HOA SV-OOA LV-OOA OA data fall into OOA-regime Aircraft never really sampled primary-dominated OA Downtown LA Redlands Long Beach f 44 : fraction from highly oxygenated OA f 43 : fraction from less oxygenated OA

OA Processing- Daytime Aging Continuous increase in OA oxidation with photochemical processing

Weekday vs. Weekend- LA Basin Less diesel traffic on weekends Decreased emission of BC on weekends

Weekday vs. Weekend- LA Basin Aging Faster chemical processing on weekends

Weekday vs. Weekend- LA Basin Similar emissions of aromatics on weekends Gasoline dominant source of aromatics

Weekday vs. Weekend- LA Basin HCs from diesel vehicles not major contributors to SOA??! Daytime, Fresh: NO x /(NO x +HNO 3 +PAN) > 0.8 Less diesel traffic on weekends OA production not lower on weekends!

SOA Production from VOCs CO (ppbv) OA (  g m 3 )  (OA/CO) obs. CO (ppbv)  (VOC/CO) obs. VOC (pptv) With aging: OA/CO↑ VOC/CO↓  (SOA i /CO) pred. 1)  (VOC i /CO) obs. SOA Yield  (SOA i /CO) pred. ?=  (OA/CO) obs. 3) 1 2) Total Predicted=  (SOA i /CO) pred.

VOC Processing- Daytime  ([VOC]/CO) (ppt/ppb)  (SOA /CO) (  g m -3 /ppb) ( * High- NO x )  (SOA /CO) (  g m -3 /ppb) ( * Low- NO x ) Benzene e e-4 Toluene e-4 1.6e-3 C8-Aromatics e-4 2.4e-3 C9-Aromatics e-4 1.0e-3 Isoprene (upper limit) e-5 7.1e-5 Monoterpenes e-4 4.8e-4 Toluene, C8- and C9- aromatics contributing most to SOA * Ng et al., ACP, 2007; Kroll et al., GRL 2005

SOA Production from VOCs- Daytime 1:1 line  (SOA i /CO) pred. ?=  (OA/CO) obs. 1 Observed  OA/CO) higher than predicted by factor of ~10 No significant change in predictability of SOA with/without diesel emissions! HCs from diesel vehicles not major contributors to SOA!!

Conclusions High correlation of OA with CO shows combustion sources as precursors of OA Photochemical processing (2-3 days) contributes to  SOA production and increase in OA/CO by a factor of 2  Increase in degree of OA oxidation by 25% Faster chemical processing over weekends leads to higher OA/CO Observed SOA are a factor of 10 higher than predicted from measured VOCs HCs from diesel emissions not so important for SOA formation?!

SOA Yields NotesHigh- NOx Yields Low-Nox Yields Benzene Toluene C8-Aromatics as xylene C9-Aromatics as toluene Isoprene Monoterpenes as a-pinene

the missing precursor? MWT=230  ([VOC]/CO) (ppt/ppb) [X], Y= [X], Y=

SOA Production- Daytime Meas./Pred D([VOC]/CO) (ppt/ppb)  (SOA /CO) (  g m -3 /ppb) (High- NO x )  (SOA /CO) (  g m -3 /ppb) (Low- NO x ) Benzene e-051.1e-4 Toluene e-41.6e-3 C8-Aromatics e-42.4e-3 C9-Aromatics e-41.0e-3 Isoprene e-57.1e-5 Monoterpenes e-44.8e-4 Pred.  (VOCs)1.7e-35.7e-3  (OA/CO)=0.02  g m -3 /ppb

SOA Production- Weekday vs. Weekend No significant change in predictability of SOA with/without diesel emissions!  (SOA /CO) (  g m -3 /ppb) (High- NO x )  (SOA /CO) (  g m -3 /ppb) (Low- NO x ) Pred.  (VOCs)2.2e-37.6e-3  (SOA /CO) (  g m -3 /ppb) (High- NO x )  (SOA /CO) (  g m -3 /ppb) (Low- NO x ) Pred.  (VOCs)9.4e-43.4e-3 Meas./Pred  (OA/CO)=0.024  g m -3 /ppb  (OA/CO)=0.010  g m -3 /ppb Meas./Pred.103.0

Weekday vs. Weekend Lower diesel-vehicle traffic on weekend- observations:  Lower NO x but higher O 3  Slightly lower VOCs (Marr et al., EST, 2002; Murphy et al., ACP, 2008)  PM 10 lower on weekend in Mexico City (Stephens et al, ACP, 2008) and LA (Qin et al., Atmos. Env., 2004)  Higher OC/EC (Harley et al., EST, 2005) Driven by lower EC on weekend Gasoline vs. diesel emission differences:  Ban-Weiss et al. (Atmos. Env., 2008) PM 2.5 emission factor higher for diesel vs. gasoline BC/OM higher for diesel PM 2.5 dominated by BC for diesel  Jakober et al. (EST, 2008) Less carbonyls in POC of diesel vs. gasoline exhaust  Miguel et al. (EST, 1998) and Geller et al. (Atmos. Env., 2006) Lighter PAHs from diesel, ultrafine and accumulation mode Heavier PAHs from gasoline, ultrafine mode

Weekday vs. Weekend- LA Basin HCs from diesel vehicles not major contributors to SOA??! Daytime, Fresh: NO x /(NO x +HNO 3 +PAN) > 0.8 Less diesel traffic on weekends OA production not lower on weekends!

OA Processing- Daytime, <1500 m

Weekday vs. Weekend- LA Basin Faster chemical processing during weekend

OA Processing- Daytime

Weekday vs. weekend