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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 WorkshopMay 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: NOx/(NOx+HNO3+PAN) > 0.8
Daytime, Aged : NOx/(NOx+HNO3+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., 2007Toluene/Benzene=3.7[OH]=2e6 molec./cm3
OA Processing- Nighttime, < 500 m
Nighttime, Fresh: NOx/(NOx+HNO3+PAN+2*N2O5+NO3) > 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
m44: fragment from highly oxygenated OAf44=m44/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
f44: fraction from highly oxygenated OAf43: 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
Agi
ng
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: NOx/(NOx+HNO3+PAN) > 0.8
Less diesel traffic on weekends OA production not lower on weekends!
SOA Production from VOCs
CO (ppbv)
OA
(g
m3 )
(OA/CO)obs.
CO (ppbv)
(VOC/CO)obs.
VO
C (
pptv
)
With aging: OA/CO↑ VOC/CO↓
(SOAi/CO)pred.1) (VOCi/CO)obs.
SOA Yield
(SOAi/CO)pred.
?=(OA/CO)obs.3) 1
2) Total Predicted=(SOAi/CO)pred.
VOC Processing- Daytime
([VOC]/CO)(ppt/ppb)
(SOA /CO)(g m-3 /ppb) (*High- NOx)
(SOA /CO)(g m-3 /ppb) (*Low- NOx)
Benzene 0.09 8.3e-05 1.1e-4
Toluene 1.38 5.9e-4 1.6e-3
C8-Aromatics 1.48 3.9e-4 2.4e-3
C9-Aromatics 0.69 3.8e-4 1.0e-3
Isoprene (upper limit) 1.12 5.8e-5 7.1e-5
Monoterpenes 0.2 1.7e-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
(SOAi/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
Notes High- NOxYields
Low-Nox Yields
Benzene 0.28 0.37
Toluene 0.11 0.3
C8-Aromatics as xylene 0.06 0.36
C9-Aromatics as toluene 0.11 0.3
Isoprene 0.018 0.022
Monoterpenes as a-pinene 0.15 0.42
the missing precursor?
MWT=230 ([VOC]/CO)(ppt/ppb)
[X], Y=0.05 40
[X], Y=0.8 1-2
SOA Production- Daytime
Meas./Pred. 11 3.3
D([VOC]/CO)(ppt/ppb)
(SOA /CO)(g m-3 /ppb) (High- NOx)
(SOA /CO)(g m-3 /ppb) (Low- NOx)
Benzene 0.09 8.3e-05 1.1e-4
Toluene 1.38 5.9e-4 1.6e-3
C8-Aromatics 1.48 3.9e-4 2.4e-3
C9-Aromatics 0.69 3.8e-4 1.0e-3
Isoprene 1.12 5.8e-5 7.1e-5
Monoterpenes 0.2 1.7e-4 4.8e-4
Pred. (VOCs) 1.7e-3 5.7e-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- NOx)
(SOA /CO)(g m-3 /ppb) (Low- NOx)
Pred. (VOCs) 2.2e-3 7.6e-3
(SOA /CO)(g m-3 /ppb) (High- NOx)
(SOA /CO)(g m-3 /ppb) (Low- NOx)
Pred. (VOCs) 9.4e-4 3.4e-3
Meas./Pred.
10 2.8
(OA/CO)=0.024 g m-3/ppb
(OA/CO)=0.010 g m-3/ppb
Meas./Pred. 10 3.0
Weekday vs. Weekend Lower diesel-vehicle traffic on weekend- observations:
Lower NOx but higher O3
Slightly lower VOCs (Marr et al., EST, 2002; Murphy et al., ACP, 2008) PM10 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) PM2.5 emission factor higher for diesel vs. gasoline BC/OM higher for diesel PM2.5 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: NOx/(NOx+HNO3+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