Observations of Aerosol Absorption and Attribution to Black Carbon, Brown Carbon, and Coating Enhancement in Wildfire Smoke during the FIREX-AQ Mission

Particulate emissions from wildfires are expected to increase in the future and to account for a larger fraction of overall emissions. The climatic impact (specifically the direct radiative effect) of the smoke depends on microphysical and optical properties of the particles and the evolution of these particles downwind of the fires. We present airborne measurements of aerosol absorption in fresh wildfire plumes sampled in a quasi-Lagrangian manner one hour to one day downwind of wildfires over the western North American in summer of 2019 during the FIREX-AQ mission. The total aerosol absorption is attributed to black carbon (BC), brown carbon (BrC) and the coating enhancement of BC absorption ("lensing"). The relative absorption due to each of these absorbers evolves downwind of the wildfires and varies between plumes depending on burning conditions. The absorption due to BC was larger than expected from bare-BC mass absorption coefficients and Mie estimates of the coating enhancement. Brown carbon absorption derived from the wavelength dependence of the total absorption and direct measurements of soluble BrC absorption are compared. The observations during FIREX-AQ are also compared to similar airborne datasets collected over the last decade.