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Examination of Brown Carbon Absorption from Wildfires in the Western U.S. during the WE-CAN Study
AMY P. SULLIVAN, Rudra Pokhrel, Yingjie Shen, Shane Murphy, Darin Toohey, Teresa Campos, Jakob Lindaas, Emily Fischer, Jeffrey Collett, Colorado State University
Abstract Number: 241
Working Group: Carbonaceous Aerosol
Abstract
Brown carbon (BrC) can potentially be a significant contributor to the visible light absorption budget. However, the contribution of particulate BrC to light absorption as well as the sources of BrC are not well understood. One major source of BrC is thought to be biomass burning. Therefore, as part of the WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen) Study we collected BrC absorption data from aboard the C-130 aircraft as it flew through smoke from wildfires occurring in the Western U.S. in July-August 2018. BrC absorption measurements were obtained by two techniques. The first coupled a Particle-into-Liquid Sampler (PILS) with a Liquid Waveguide Capillary Cell and a Total Organic Carbon analyzer for near real-time measurements of BrC absorption and WSOC (water-soluble organic carbon). The second employed a custom-built Photoacoustic Aerosol Absorption Spectrometer (PAS) to measure total absorption at red and blue wavelengths and then calculate black carbon and BrC absorption. Airborne results from these measurements for a number of different wildfires will be presented. A high correlation was found between WSOC and BrC absorption for wildfire smoke. It was also observed that the fraction of the BrC absorption in wildfire smoke due to water-soluble species was ~45%. When using calculated particle mass concentrations, provided by UHSAS (Ultra-High-Sensitivity Aerosol Spectrometer) measurements, to account for the non-water-soluble fraction of BrC absorption, good closure was found between the absorption determined by the PAS and PILS measurements when accounting for the differences in particle vs. bulk solution absorption. In addition, the relationship between the BrC absorption and known smoke markers will be examined. How parameters such as aging and fire dynamics might play a role on the BrC absorption from wildfires will also be discussed.