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Discussion papers
https://doi.org/10.5194/acp-2019-594
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-594
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Jul 2019

Research article | 02 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Modeling global radiative effect of brown carbon: A larger heating source in the tropical free troposphere than black carbon

Aoxing Zhang1, Yuhang Wang1, Yuzhong Zhang1,a, Rodney J. Weber1, Yongjia Song1, Ziming Ke1,b, and Yufei Zou1,c Aoxing Zhang et al.
  • 1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, USA
  • anow at: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • bnow at: Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming, USA
  • cnow at: School of Environmental and Forest Sciences, University of Washington, Seattle, WA, USA

Abstract. Carbonaceous aerosols significantly affect global radiative forcing and climate through absorption and scattering of sunlight. Black carbon (BC) and brown carbon (BrC) are light-absorbing carbonaceous aerosols. The direct radiative effect (DRE) of BrC is uncertain. A recent study suggests that BrC absorption is comparable to BC in the upper troposphere over biomass burning regions and that the resulting radiative heating tends to stabilize the atmosphere. Yet current climate models do not include proper physical and chemical treatments of BrC. In this study, we derived a BrC global biomass burning emission inventory on the basis of the Global Fire Emissions Database 4 (GFED4), developed a BrC module in the Community Atmosphere Model version 5 (CAM5) of Community Earth System Model (CESM) model, and investigated the photo-bleaching effect and convective transport of BrC on the basis of Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and Deep Convective Clouds and Chemistry Project (DC-3) measurements. The model simulations of BC were also evaluated using HIAPER (High-Performance Instrumented Airborne Platform for Environmental Research) Pole-to-Pole Observations (HIPPO) measurements. We found that globally BrC is a significant absorber, the DRE of which is 0.10 W/m2, more than 25 % of BC DRE (+0.39 W/m2). Most significantly, model results indicated that BrC atmospheric heating in the tropical mid and upper troposphere is larger than that of BC. The source of tropical BrC is mainly from wildfires, which are more prevalent in the tropical regions than higher latitudes and release much more BrC relative to BC than industrial sources. While BC atmospheric heating is skewed towards northern mid-latitude lower atmosphere, BrC heating is more centered in the tropical free troposphere. The contribution of BrC heating to the Hadley circulation and latitudinal expansion of the tropics is comparable to BC heating.

Aoxing Zhang et al.
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Short summary
Black carbon (BC) and Brown carbon (BrC) are light-absorbing carbonaceous aerosols. We developed a module to simulate the emissions, atmospheric processing, and the direct radiative effect of BrC in the Community Earth System Model. We found that globally BrC is a significant absorber, and is more centered in the tropical free troposphere compared to BC. The contribution of BrC heating to the Hadley circulation and latitudinal expansion of the tropics is comparable to BC heating.
Black carbon (BC) and Brown carbon (BrC) are light-absorbing carbonaceous aerosols. We developed...
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