10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

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Brown Carbon Aerosol Observed in the Remote Atmosphere

LINGHAN ZENG, Rodney J. Weber, Aoxing Zhang, Yuhang Wang, Eric Scheuer, Jack Dibb, Jose-Luis Jimenez, Pedro Campuzano-Jost, Joshua P. Schwarz, Kathryn McKain, Eric Apel, Georgia Institute of Technology

     Abstract Number: 1355
     Working Group: Carbonaceous Aerosol

Abstract
Organic aerosols (OA) have long been thought to only scatter sun light and thereby cool the climate. However, a portion of organics, so called brown carbon (BrC) absorb strongly at shorter wavelengths. BrC is emitted by the incomplete combustion of fuels, especially biomass, or produced from secondary formation processes. BrC has been found to be ubiquitous in continental air masses. In both ambient and laboratory studies, as BrC ages, it is observed to become less effective as a light-absorber due to photo-bleaching effects. The global radiative impact of BrC is difficult to assess with models owing to the large uncertainties in its emissions and chemical processing in the atmosphere. Lack of global scale BrC data sets limits our understanding of BrC processing and precludes meaningful model simulation assessments. The NASA Atmospheric Tomography (ATom) mission provided an opportunity to make measurements of BrC in the remote atmosphere over global extents reaching near pole-to-pole along the central Pacific and Atlantic oceans during different seasons. During ATom, filters loaded with ambient aerosol sampled with the NASA DC-8 research aircraft were extracted into water and methanol, sequentially, and the light absorption of the solutes was determined via long optical path capillary measurements. The results provide the first data set of BrC on a global scale. Generally, BrC concentrations are found to be very low in most of the remote atmosphere, and detectible levels were only found in specific regions, including the mid-Atlantic downwind of African or South American fires and in regions of the Arctic. Further data analysis, including comparisons with predictions from the Community Atmosphere Model version 5 (CAM5) of the Community Earth System Model (CESM) are used to better understand the sources, atmospheric loss and transport processes, and radiative impacts of BrC on a global scale.