AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Free Tropospheric Brown Carbon: Radiative Impact and Sources
YUZHONG ZHANG, Haviland Forrister, Yuhang Wang, Athanasios Nenes, Rodney J. Weber, Georgia Institute of Technology
Abstract Number: 466 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Observations from recent aircraft campaigns over the continental United States (DC3, SEAC4RS) have shown that brown carbon (BrC) is prevalent in the troposphere, and enriched with respect to BC at high altitude (5—12 km). However, the radiative impact and sources of this high-altitude BrC is largely unknown. Using radiative transfer calculations constrained by DC3 and SEAC4RS observations, we find that BrC (3.5 Wm-2) can be responsible for ~ 35% of the instantaneous (noontime, solar zenith angle 25°) radiative absorption at the tropopause by aerosols (10 Wm-2). Although the concentration of BrC at high altitude was lower than that at low altitude (<5 km), they contributed almost equally to the radiative forcing at the tropopause, underscoring the radiative impact of high-altitude BrC. Analysis of DC3 deep convection data shows that BrC in outflow was ~ 70% of that in inflow. In contrast, only ~ 25% BC got through. This suggests that deep convection may be an important transport mechanism of BrC to high altitudes. The mechanism may also involve processing by ice cloud and/or condensation of semi-volatile compounds.