Brown Carbon Lifetime and Chemistry in Aged Wildfire Plumes from the Western U.S.

Wildfires are a major source of brown carbon (organic aerosol that absorbs strongly in the ultraviolet and visible spectral regions) in the United States and globally. The lifetime and chemical aging of brown carbon aerosol from wildfires are important, but poorly known. Three new instruments measured water-soluble brown carbon absorption in wildfire smoke in the western U.S. during the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen (WE-CAN 2018) and the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ 2019) field campaigns. These instruments were deployed on the NSF C-130, NASA DC-8, and NOAA Twin Otter aircraft. In this presentation, we report the lifetime of brown carbon for eleven fire plumes sampled by the NOAA Twin Otter with transport times of 0.5 5 hours. Analysis of fire radiative power shows that the fire conditions were relatively constant, and that the plume sampling was semi-Lagrangian. The lifetime of brown carbon varied in the fire plumes, and it was not rapidly removed as plumes aged. To better understand the chemical aging of brown carbon, we examine the spectral dependence of the absorption and identify possible chemical contributors.