How much of the global aerosol optical depth is found in the boundary layer and free troposphere?
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Published:2018-06-01
Issue:10
Volume:18
Page:7709-7720
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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:
Bourgeois Quentin, Ekman Annica M. L.ORCID, Renard Jean-Baptiste, Krejci RadovanORCID, Devasthale Abhay, Bender Frida A.-M., Riipinen Ilona, Berthet GwenaëlORCID, Tackett Jason L.
Abstract
Abstract. The global aerosol extinction from the CALIOP space lidar was used to compute
aerosol optical depth (AOD) over a 9-year period (2007–2015) and
partitioned between the boundary layer (BL) and the free troposphere (FT)
using BL heights obtained from the ERA-Interim archive. The results show that
the vertical distribution of AOD does not follow the diurnal cycle of the BL
but remains similar between day and night highlighting the presence of a
residual layer during night. The BL and FT contribute 69 and 31 %,
respectively, to the global tropospheric AOD during daytime in line with
observations obtained in Aire sur l'Adour (France) using the Light Optical
Aerosol Counter (LOAC) instrument. The FT AOD contribution is larger in the
tropics than at mid-latitudes which indicates that convective transport
largely controls the vertical profile of aerosols. Over oceans, the FT AOD
contribution is mainly governed by long-range transport of aerosols from
emission sources located within neighboring continents. According to the
CALIOP aerosol classification, dust and smoke particles are the main aerosol
types transported into the FT. Overall, the study shows that the fraction of
AOD in the FT – and thus potentially located above low-level clouds – is
substantial and deserves more attention when evaluating the radiative effect
of aerosols in climate models. More generally, the results have implications
for processes determining the overall budgets, sources, sinks and transport
of aerosol particles and their description in atmospheric models.
Funder
Swedish National Space Agency
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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