Present-day radiative effect from radiation-absorbing aerosols in snow
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Published:2021-05-06
Issue:9
Volume:21
Page:6875-6893
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Tuccella Paolo, Pitari Giovanni, Colaiuda ValentinaORCID, Raparelli Edoardo, Curci GabrieleORCID
Abstract
Abstract. Black carbon (BC), brown carbon (BrC), and soil
dust are the most important radiation-absorbing aerosols (RAAs). When RAAs are deposited on the snowpack, they lower the snow albedo, causing an increase in
the solar radiation absorption. The climatic impact associated with the snow
darkening induced by RAAs is highly uncertain. The Intergovernmental Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) attributes low
and medium confidence to radiative forcing (RF) from BrC and dust in snow,
respectively. Therefore, the contribution of anthropogenic sources and
carbonaceous aerosols to RAA RF in snow is not clear. Moreover, the snow
albedo perturbation induced by a single RAA species depends on the presence
of other light-absorbing impurities contained in the snowpack. In this work, we calculated the present-day RF of RAAs in snow starting from the deposition
fields from a 5-year simulation with the GEOS-Chem global chemistry and
transport model. RF was estimated taking into account the presence of BC,
BrC, and mineral soil dust in snow, simultaneously. Modeled BC and black
carbon equivalent (BCE) mixing ratios in snow and the fraction of light
absorption due to non-BC compounds (fnon-BC) were compared with
worldwide observations. We showed that BC, BCE, and fnon-BC, obtained from
deposition and precipitation fluxes, reproduce the regional variability and
order of magnitude of the observations. Global-average all-sky total RAA-,
BC-, BrC-, and dust-snow RF were 0.068, 0.033, 0.0066, and
0.012 W m−2,
respectively. At a global scale, non-BC compounds accounted for 40 % of RAA-snow RF, while anthropogenic RAAs contributed to the forcing for 56 %.
With regard to non-BC compounds, the largest impact of BrC has been found
during summer in the Arctic (+0.13 W m−2). In the middle latitudes of
Asia, the forcing from dust in spring accounted for 50 % (+0.24 W m−2) of the total RAA RF. Uncertainties in absorbing optical
properties, RAA mixing ratio in snow, snow grain dimension, and snow cover
fraction resulted in an overall uncertainty of −50 %/+61 %,
−57 %/+183 %, −63 %/+112 %, and −49 %/+77 % in BC-, BrC-,
dust-, and total RAA-snow RF, respectively. Uncertainty upper bounds of BrC
and dust were about 2 and 3 times larger than the upper bounds associated with
BC. Higher BrC and dust uncertainties were mainly due to the presence of
multiple absorbing impurities in the snow. Our results highlight that an
improvement of the representation of RAAs in snow is desirable, given the
potential high efficacy of this forcing.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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