Brown carbon (BrC) is an organic aerosol material that preferentially
absorbs light of shorter wavelengths. Global-scale radiative impacts of
BrC have been difficult to assess due to the lack of BrC observational
data. To address this, aerosol filters were continuously collected with
near pole-to-pole latitudinal coverage over the Pacific and Atlantic
basins in three seasons as part of the Atmospheric Tomography Mission.
BrC chromophores in filter extracts were measured. We find that
globally, BrC was highly spatially heterogeneous, mostly detected in air
masses that had been transported from regions of extensive biomass
burning. We calculate the average direct radiative effect due to BrC
absorption accounted for approximately 7 to 48% of the top of the
atmosphere clear sky instantaneous forcing by all absorbing carbonaceous
aerosols in the remote atmosphere, indicating that BrC from biomass
burning is an important component of the global radiative balance.