In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 18, No. 17 ( 2018-09-14), p. 13265-13281
Abstract:
Abstract. We present estimates of changes in the direct aerosol effects (DRE) and its
anthropogenic component (DRF) from 2001 to 2015 using the GFDL
chemistry–climate model AM3 driven by CMIP6 historical emissions. AM3 is
evaluated against observed changes in the clear-sky shortwave direct aerosol
effect (DREswclr) derived from the Clouds and
the Earth's Radiant Energy System (CERES) over polluted regions. From 2001 to
2015, observations suggest that DREclrsw
increases (i.e., less radiation is scattered to space by aerosols) over
western Europe (0.7–1 W m−2 decade−1) and the eastern US
(0.9–1.4 W m−2 decade−1), decreases over India (−1 to
−1.6 W m−2 decade−1), and does not change significantly over
eastern China. AM3 captures these observed regional changes in
DREclrsw well in the US and western Europe,
where they are dominated by the decline of sulfate aerosols, but not in Asia,
where the model overestimates the decrease of
DREclrsw. Over India, the model bias can be
partly attributed to a decrease of the dust optical depth, which is not
captured by our model and offsets some of the increase of anthropogenic
aerosols. Over China, we find that the decline of SO2 emissions
after 2007 is not represented in the CMIP6 emission inventory. Accounting for
this decline, using the Modular Emission Inventory for China, and for the
heterogeneous oxidation of SO2 significantly reduces the model
bias. For both India and China, our simulations indicate that nitrate and
black carbon contribute more to changes in
DREclrsw than in the US and Europe. Indeed,
our model suggests that black carbon (+0.12 W m−2) dominates the
relatively weak change in DRF from 2001 to 2015 (+0.03 W m−2). Over
this period, the changes in the forcing from nitrate and sulfate are both
small and of the same magnitude (−0.03 W m−2 each). This is in sharp
contrast to the forcing from 1850 to 2001 in which forcings by sulfate and
black carbon largely cancel each other out, with minor contributions from
nitrate. The differences between these time periods can be well understood
from changes in emissions alone for black carbon but not for nitrate and
sulfate; this reflects non-linear changes in the photochemical production of
nitrate and sulfate associated with changes in both the magnitude and spatial
distribution of anthropogenic emissions.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-18-13265-2018
DOI:
10.5194/acp-18-13265-2018-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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