Preprints
https://doi.org/10.5194/acp-2022-459
https://doi.org/10.5194/acp-2022-459
 
01 Jul 2022
01 Jul 2022
Status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Examination of Brown Carbon Absorption from Wildfires in the Western U.S. During the WE-CAN Study

Amy P. Sullivan1, Rudra P. Pokhrel2,a, Yingjie Shen2, Shane M. Murphy2, Darin W. Toohey3, Teresa Campos4, Jakob Lindaas1, Emily V. Fischer1, and Jeffrey L. Collett Jr.1 Amy P. Sullivan et al.
  • 1Colorado State University, Department of Atmospheric Science, Fort Collins, Colorado 80523
  • 2University of Wyoming, Department of Atmospheric Science, Laramie, WY 82071
  • 3University of Colorado – Boulder, Department of Atmospheric and Oceanic Sciences, Boulder, CO 80309
  • 4National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO
  • anow at: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 and NOAA Chemical Science Laboratory, Boulder, CO 80305

Abstract. Light absorbing organic carbon, or brown carbon (BrC), can be a significant contributor to the visible light absorption budget. However, the sources of BrC and the contributions of BrC to light absorption are not well understood. Biomass burning is thought to be a major source of BrC. Therefore, as part of the WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen) Study BrC absorption data was collected aboard the NSF/NCAR C-130 aircraft as it intercepted smoke from wildfires in the Western U.S. in July–August 2018. BrC absorption measurements were obtained in near real-time using two techniques. The first coupled a Particle-into-Liquid Sampler (PILS) with a Liquid Waveguide Capillary Cell and a Total Organic Carbon analyzer for measurements of water-soluble BrC absorption and WSOC (water-soluble organic carbon). The second employed a custom-built Photoacoustic Aerosol Absorption Spectrometer (PAS) to measure total absorption at 405 and 660 nm. The PAS BrC absorption at 405 nm (PAS total Abs 405 BrC) was calculated by assuming the absorption determined by the PAS at 660 nm was equivalent to the black carbon (BC) absorption and the BC aerosol absorption Ångström exponent was 1. Data from the PILS and PAS were combined to investigate the water-soluble vs. total BrC absorption at 405 nm in the various wildfire plumes sampled during WE-CAN. WSOC, PILS water-soluble Abs 405, and PAS total Abs 405 tracked each other in and out of the smoke plumes. BrC absorption was correlated with WSOC (R2 value for PAS = 0.42 and PILS = 0.60) and CO (carbon monoxide) (R2 value for PAS = 0.76 and PILS = 0.55) for all wildfires sampled. The PILS water-soluble Abs 405 was corrected for the non-water-soluble fraction of the aerosol using the calculated UHSAS (Ultra-High-Sensitivity Aerosol Spectrometer) aerosol mass. The corrected PILS water-soluble Abs 405 showed good closure with the PAS total Abs 405 BrC with a factor of ~1.5 to 2 difference. This difference was explained by particle vs. bulk solution absorption measured by the PAS vs. PILS, respectively, and confirmed by Mie Theory calculations. During WE-CAN, ~45 % (ranging from 31 % to 65 %) of the BrC absorption was observed to be due to water-soluble species. The ratio of BrC absorption to WSOC or ΔCO showed no clear dependence on fire dynamics or the time since emission over 9 h.

Amy P. Sullivan et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-459', Anonymous Referee #1, 20 Jul 2022
  • RC2: 'Comment on acp-2022-459', Anonymous Referee #2, 30 Jul 2022
  • RC3: 'Comment on acp-2022-459', Anonymous Referee #3, 06 Aug 2022
  • AC1: 'Response to Reviewer Comments', Amy Sullivan, 23 Sep 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-459', Anonymous Referee #1, 20 Jul 2022
  • RC2: 'Comment on acp-2022-459', Anonymous Referee #2, 30 Jul 2022
  • RC3: 'Comment on acp-2022-459', Anonymous Referee #3, 06 Aug 2022
  • AC1: 'Response to Reviewer Comments', Amy Sullivan, 23 Sep 2022

Amy P. Sullivan et al.

Amy P. Sullivan et al.

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Short summary
During the WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen) Study brown carbon (BrC) absorption was measured on the NSF/NCAR C-130 aircraft using a Particle-into-Liquid Sampler and Photoacoustic Aerosol Absorption Spectrometer. Approximately 45 % of the BrC absorption in wildfires was observed to be due to water-soluble species. The ratio of BrC absorption to WSOC or ΔCO showed no clear dependence on fire dynamics or the time since emission over 9 h.
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