characterization of organic aerosol formation and processing in california from airborne...

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


Agi

ng

Faster chemical processing on weekends


Similar emissions of aromatics on weekends Gasoline dominant source of aromatics


HCs from diesel vehicles not major contributors to SOA??!


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!



Pred. (VOCs) 2.2e-3 7.6e-3



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


HCs from diesel vehicles not major contributors to SOA??!


Less diesel traffic on weekends OA production not lower on weekends!

OA Processing- Daytime, <1500 m


Faster chemical processing during weekend

OA Processing- Daytime

Weekday vs. weekend

characterization of organic aerosol formation and processing in california from airborne...

Documents

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cm3oa processing nighttime

co la flights

weekend la basin hcs

diesel vehicles

oxygenated oaf44

oxygenated oaf43

oa oxidation