Modeling the global radiative effect of brown carbon: a potentially larger heating source in the tropical free troposphere than black carbon
<p>Carbonaceous aerosols significantly affect global radiative forcing and climate through absorption and the 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 sugges...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/20/1901/2020/acp-20-1901-2020.pdf |
| Summary: | <p>Carbonaceous aerosols significantly affect global
radiative forcing and climate through absorption
and the 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 version 4 (GFED4),
developed a module to simulate the light absorption of BrC in the Community
Atmosphere Model version 5 (CAM5) of the Community Earth System Model (CESM), and investigated the photobleaching 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 (DC3) 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 m<span class="inline-formula"><sup>−2</sup></span>, more than 25 % of BC DRE (<span class="inline-formula">+0.39</span> W m<span class="inline-formula"><sup>−2</sup></span>).
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 the northern mid-latitude lower atmosphere, BrC heating is more centered in the
tropical free troposphere. A possible mechanism for the enhanced convective
transport of BrC is that hydrophobic high molecular weight BrC becomes a
larger fraction of the BrC and less easily activated in a cloud as the
aerosol ages. The contribution of BrC heating to the Hadley circulation and
latitudinal expansion of the tropics is likely comparable to BC heating.</p> |
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| ISSN: | 1680-7316 1680-7324 |