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Complexity in the Evolution, Composition, and Spectroscopy of Brown Carbon in Aircraft Measurements of Wildfire Plumes

Washenfelder, R. A. and Azzarello, L. and Ball, K. and Brown, S. S. and Decker, Z. C. J. and Franchin, A. and Fredrickson, C. D. and Hayden, K. and Holmes, C. D. and Middlebrook, A. M. and Palm, B. B. and Pierce, R. B. and Price, D. J. and Roberts, J. M. and Robinson, M. A. and Thornton, J. A. and Womack, C. C. and Young, C. J. (2022) Complexity in the Evolution, Composition, and Spectroscopy of Brown Carbon in Aircraft Measurements of Wildfire Plumes. Geophysical Research Letters, 49 (9). Art. No. e2022GL098951. ISSN 0094-8276. doi:10.1029/2022gl098951.

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Biomass burning is a major source of light-absorbing organic aerosol (brown carbon), but its composition, chemical evolution, and lifetime are not well known. We measured water-soluble brown carbon absorption from 310 to 500 nm on the National Oceanic and Atmospheric Administration Twin Otter aircraft during flights downwind of western United States wildfires in summer 2019. The sampling strategy was near-Lagrangian and the plume ages spanned 0–5 hr. Trends in brown carbon mass absorption coefficient with plume age varied between flights, and did not show an exponential decay over these short time scales. The measured absorption spectra were smoothly varying, without identifiable contributions from individual chromophores with structured absorption. Using aerosol tracer ions and reference absorption spectra, the calculated contribution of 4-nitrocatechol to total absorption was <22 ± 9% and <11 ± 5%, although spectral fitting showed that it may be as low as <1.1% and <0.6% at 365 and 405 nm, respectively.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemData
Washenfelder, R. A.0000-0002-8106-3702
Brown, S. S.0000-0001-7477-9078
Decker, Z. C. J.0000-0001-9604-8671
Franchin, A.0000-0001-7425-8272
Fredrickson, C. D.0000-0002-9127-5258
Holmes, C. D.0000-0002-2727-0954
Middlebrook, A. M.0000-0002-2984-6304
Palm, B. B.0000-0001-5548-0812
Pierce, R. B.0000-0002-2767-1643
Price, D. J.0000-0003-3693-1475
Roberts, J. M.0000-0002-8485-8172
Robinson, M. A.0000-0003-0977-9148
Thornton, J. A.0000-0002-5098-4867
Womack, C. C.0000-0002-7101-9054
Young, C. J.0000-0002-6908-5829
Alternate Title:Brown carbon from wildfire plumes
Additional Information:© 2022 American Geophysical Union. Issue Online: 05 May 2022; Version of Record online: 05 May 2022; Accepted manuscript online: 11 April 2022; Manuscript accepted: 05 April 2022; Manuscript received: 30 March 2022. We thank Carsten Warneke, Joshua Schwarz, James Crawford, and Jack Dibb for organizing the FIREX-AQ field campaign. We thank the NOAA Aircraft Operations Center for support during the field mission. R. A. Washenfelder thanks Rodney Weber and Linghan Zeng for information about the solubility of BrC in biomass burning plumes, and Amy Sullivan and Nick Wagner for helpful discussions. This project was supported by the NOAA Atmospheric Chemistry, Carbon, and Climate Program (AC4). Z. C. J. Decker was supported by a graduate research award at the University of Colorado CIRES. L. Azzarello was supported by a Mitacs Globalink Research Internship and an NSERC Discovery Grant. The AMS calibration work was supported by NASA grant 17-ACLS17-0014. Data Availability Statement: The aircraft data used in the study are publicly available at
Funding AgencyGrant Number
National Oceanic and Atmospheric Administration (NOAA)UNSPECIFIED
University of ColoradoUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Subject Keywords:Fire Influence on Regional to Global Environments and Air Quality; FIREX-AQ; biomass burning; wildfire smoke; brown carbon; aerosol absorption
Issue or Number:9
Classification Code:0365 (Troposphere: composition and chemistry), 0305 (Aerosols and particles), 0322 (Constituent sources and sinks), 0345 (Pollution: urban and regional), 0317 (Chemical kinetic and photochemical properties)
Record Number:CaltechAUTHORS:20220414-26504000
Persistent URL:
Official Citation:Washenfelder, R. A., Azzarello, L., Ball, K., Brown, S. S., Decker, Z. C. J., Franchin, A., et al. (2022). Complexity in the evolution, composition, and spectroscopy of brown carbon in aircraft measurements of wildfire plumes. Geophysical Research Letters, 49, e2022GL098951.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114307
Deposited By: George Porter
Deposited On:18 Apr 2022 23:08
Last Modified:10 May 2022 22:36

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