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Concentrations and sources of organic carbon aerosols in the free troposphere over North America

Heald, Colette L. and Jacob, Daniel J. and Turquety, Solène and Hudman, Rynda C. and Weber, Rodney J. and Sullivan, Amy P. and Peltier, Richard E. and Atlas, Eliot L. and de Gouw, Joost A. and Warneke, Carsten and Holloway, John S. and Neuman, J. Andrew and Flocke, Frank M. and Seinfeld, John H. (2006) Concentrations and sources of organic carbon aerosols in the free troposphere over North America. Journal of Geophysical Research. Atmospheres, 111 (D23). Art. No. D23S47. ISSN 2169-897X. doi:10.1029/2006JD007705.

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Aircraft measurements of water-soluble organic carbon (WSOC) aerosol over NE North America during summer 2004 (ITCT-2K4) are simulated with a global chemical transport model (GEOS-Chem) to test our understanding of the sources of organic carbon (OC) aerosol in the free troposphere (FT). Elevated concentrations were observed in plumes from boreal fires in Alaska and Canada. WSOC aerosol concentrations outside of these plumes average 0.9 ± 0.9 μg C m⁻³ in the FT (2–6 km). The corresponding model value is 0.7 ± 0.6 μg C m⁻³, including 42% from biomass burning, 36% from biogenic secondary organic aerosol (SOA), and 22% from anthropogenic emissions. Previous OC aerosol observations over the NW Pacific in spring 2001 (ACE-Asia) averaged 3.3 ± 2.8 μg C m⁻³ in the FT, compared to a model value of 0.3 ± 0.3 μg C m⁻³. WSOC aerosol concentrations in the boundary layer (BL) during ITCT-2K4 are consistent with OC aerosol observed at the IMPROVE surface network. The model is low in the boundary layer by 30%, which we attribute to secondary formation at a rate comparable to primary anthropogenic emission. Observed WSOC aerosol concentrations decrease by a factor of 2 from the BL to the FT, as compared to a factor of 10 decrease for sulfate, indicating that most of the WSOC aerosol in the FT originates in situ. Despite reproducing mean observed WSOC concentrations in the FT to within 25%, the model cannot account for the variance in the observations (R = 0.21). Covariance analysis of FT WSOC aerosol with other measured chemical variables suggests an aqueous-phase mechanism for SOA generation involving biogenic precursors.

Item Type:Article
Related URLs:
URLURL TypeDescription
Heald, Colette L.0000-0003-2894-5738
Jacob, Daniel J.0000-0002-6373-3100
Turquety, Solène0000-0002-0398-547X
Weber, Rodney J.0000-0003-0765-8035
Sullivan, Amy P.0000-0003-0143-8197
Peltier, Richard E.0000-0002-0402-0979
de Gouw, Joost A.0000-0002-0385-1826
Warneke, Carsten0000-0003-3811-8496
Holloway, John S.0000-0002-4585-9594
Neuman, J. Andrew0000-0002-3986-1727
Flocke, Frank M.0000-0002-2661-6394
Seinfeld, John H.0000-0003-1344-4068
Additional Information:This work was supported by the U.S. Environmental Protection Agency STAR program, the Electrical Power Research Institute (EPRI), and a NOAA Postdoctoral Fellowship in Climate and Global Change for CLH, administered by the University Corporation for Atmospheric Research. We thank Rokjin Park and Daven Henze for useful discussions.
Funding AgencyGrant Number
Environmental Protection Agency (EPA)UNSPECIFIED
Electric Power Research Institute (EPRI)UNSPECIFIED
National Oceanic and Atmospheric Administration (NOAA)UNSPECIFIED
Issue or Number:D23
Record Number:CaltechAUTHORS:HEAgpr06.234
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7956
Deposited By: Stephanie Chang
Deposited On:15 Feb 2023 23:51
Last Modified:15 Feb 2023 23:51

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