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Particulate brown carbon (BrC) in the atmosphere absorbs light at subvisible wavelengths and has poorly constrained but potentially large climate forcing impacts. BrC from biomass burning has virtually unknown lifecycle and atmospheric stability. Here, BrC emitted from intense wildfires was measured in plumes transported over 2 days from two main fires, during the 2013 NASA SEAC4RS mission. Concurrent measurements of organic aerosol (OA) and black carbon (BC) mass concentration, BC coating thickness, absorption Angstrom exponent, and OA oxidation state reveal that the initial BrC emitted from the fires was largely unstable. Using back trajectories to estimate the transport time indicates that BrC aerosol light absorption decayed in the plumes with a half-life of 9 to 15 h, measured over day and night. Although most BrC was lost within a day, possibly through chemical loss and/or evaporation, the remaining persistent fraction likely determines the background BrC levels most relevant for climate forcing.

Little is known about the optical significance of light absorbing particulate organic compounds (i.e., brown carbon, BrC), including the importance relative to black carbon (BC) and influence on direct radiative forcing by aerosols. The vertical profile of BrC affects its radiative forcing, yet the distribution of BrC in the free troposphere is largely unknown. In this study, BrC absorption was directly measured in solvent extracts of particulate filters obtained from aircraft sampling over the continental USA. Excluding biomass burning plumes, BrC was observed throughout the tropospheric column (