Abstract View
Brown Carbon Global Direct Radiative Effects
LINGHAN ZENG, Aoxing Zhang, Yuhang Wang, Nick Wagner, Joseph Katich, Joshua P. Schwarz, Gregory Schill, Charles Brock, Karl D. Froyd, Daniel Murphy, Christina Williamson, Agnieszka Kupc, Eric Scheuer, Jack Dibb, Rodney J. Weber, Georgia Institute of Technology
Abstract Number: 392
Working Group: Carbonaceous Aerosol
Abstract
Organic aerosols (OA) mostly scatter solar radiation cooling the planet. However, a portion of organic species, brown carbon (BrC), absorbs light at shorter visible and near-ultraviolet wavelengths. BrC is emitted directly by the incomplete combustion of fuels, especially biomass and biofuel burning, or from secondary formation processes. Globally, the radiative impacts of BrC are difficult to assess due to the lack of BrC observational data. To address this, filter samples were collected on the NASA DC-8 research aircraft with near pole-to-pole latitudinal coverage over the Pacific and Atlantic basins in three seasons as part of the Atmospheric Tomography Mission (ATom). These filters were sequentially extracted into water then methanol and the light absorption of the solutes measured with a spectrophotometer. The results provide the first data set of BrC on a global scale. We find that BrC concentrations were highly spatially heterogeneous with levels below the detection limits (0.05 to 0.15 Mm-1) in most of the remote atmosphere, whereas levels above the detection limit were observed in air masses that had been transported from regions of biomass burning. The impact of BrC was assessed with a radiative transfer model for the measurement regions. The direct radiative effect due to BrC absorption accounted for approximately up to 48% of top of the atmosphere clear sky instantaneous forcing due to absorbing carbonaceous aerosols. These results show that BrC from biomass burning is an important component of the global radiative balance.