Interpreting the ultraviolet aerosol index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects
Satellite observations of the ultraviolet aerosol index (UVAI) are sensitive to absorption of solar radiation by aerosols; this absorption affects photolysis frequencies and radiative forcing. We develop a global simulation of the UVAI using the 3-D chemical transport model GEOS-Chem coupled with...
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doaj-7ede24468176428b8aef016646ded4b62020-11-24T20:56:58ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242016-03-01162507252310.5194/acp-16-2507-2016Interpreting the ultraviolet aerosol index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effectsM. S. Hammer0R. V. Martin1R. V. Martin2A. van Donkelaar3V. Buchard4V. Buchard5O. Torres6D. A. Ridley7R. J. D. Spurr8Department of Physics and Atmospheric Science, Dalhousie University, Halifax, CanadaDepartment of Physics and Atmospheric Science, Dalhousie University, Halifax, CanadaHarvard-Smithsonian Center for Astrophysics, Cambridge, MA, USADepartment of Physics and Atmospheric Science, Dalhousie University, Halifax, CanadaNASA/Goddard Space Flight Center, Greenbelt, MD, USAGESTAR/Universities Space Research Association, Columbia, MD, USANASA/Goddard Space Flight Center, Greenbelt, MD, USADepartment of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USART Solutions, Inc., 9 Channing Street, Cambridge, MA, USASatellite observations of the ultraviolet aerosol index (UVAI) are sensitive to absorption of solar radiation by aerosols; this absorption affects photolysis frequencies and radiative forcing. We develop a global simulation of the UVAI using the 3-D chemical transport model GEOS-Chem coupled with the Vector Linearized Discrete Ordinate Radiative Transfer model (VLIDORT). The simulation is applied to interpret UVAI observations from the Ozone Monitoring Instrument (OMI) for the year 2007. Simulated and observed values are highly consistent in regions where mineral dust dominates the UVAI, but a large negative bias (−0.32 to −0.97) exists between simulated and observed values in biomass burning regions. We determine effective optical properties for absorbing organic aerosol, known as brown carbon (BrC), and implement them into GEOS-Chem to better represent observed UVAI values over biomass burning regions. The inclusion of absorbing BrC decreases the mean bias between simulated and OMI UVAI values from −0.57 to −0.09 over West Africa in January, from −0.32 to +0.0002 over South Asia in April, from −0.97 to −0.22 over southern Africa in July, and from −0.50 to +0.33 over South America in September. The spectral dependence of absorption after including BrC in the model is broadly consistent with reported observations for biomass burning aerosol, with absorbing Ångström exponent (AAE) values ranging from 2.9 in the ultraviolet (UV) to 1.3 across the UV–Near IR spectrum. We assess the effect of the additional UV absorption by BrC on atmospheric photochemistry by examining tropospheric hydroxyl radical (OH) concentrations in GEOS-Chem. The inclusion of BrC decreases OH by up to 30 % over South America in September, up to 20 % over southern Africa in July, and up to 15 % over other biomass burning regions. Global annual mean OH concentrations in GEOS-Chem decrease due to the presence of absorbing BrC, increasing the methyl chloroform lifetime from 5.62 to 5.68 years, thus reducing the bias against observed values. We calculate the direct radiative effect (DRE) of BrC using GEOS-Chem coupled with the radiative transfer model RRTMG (GC-RT). Treating organic aerosol as containing more strongly absorbing BrC changes the global annual mean all-sky top of atmosphere (TOA) DRE by +0.03 W m<sup>−2</sup> and all-sky surface DRE by −0.08 W m<sup>−2</sup>. Regional changes of up to +0.3 W m<sup>−2</sup> at TOA and down to −1.5 W m<sup>−2</sup> at the surface are found over major biomass burning regions.https://www.atmos-chem-phys.net/16/2507/2016/acp-16-2507-2016.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
M. S. Hammer R. V. Martin R. V. Martin A. van Donkelaar V. Buchard V. Buchard O. Torres D. A. Ridley R. J. D. Spurr |
spellingShingle |
M. S. Hammer R. V. Martin R. V. Martin A. van Donkelaar V. Buchard V. Buchard O. Torres D. A. Ridley R. J. D. Spurr Interpreting the ultraviolet aerosol index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects Atmospheric Chemistry and Physics |
author_facet |
M. S. Hammer R. V. Martin R. V. Martin A. van Donkelaar V. Buchard V. Buchard O. Torres D. A. Ridley R. J. D. Spurr |
author_sort |
M. S. Hammer |
title |
Interpreting the ultraviolet aerosol index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects |
title_short |
Interpreting the ultraviolet aerosol index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects |
title_full |
Interpreting the ultraviolet aerosol index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects |
title_fullStr |
Interpreting the ultraviolet aerosol index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects |
title_full_unstemmed |
Interpreting the ultraviolet aerosol index observed with the OMI satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects |
title_sort |
interpreting the ultraviolet aerosol index observed with the omi satellite instrument to understand absorption by organic aerosols: implications for atmospheric oxidation and direct radiative effects |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2016-03-01 |
description |
Satellite observations of the ultraviolet aerosol index (UVAI) are sensitive
to absorption of solar radiation by aerosols; this absorption affects
photolysis frequencies and radiative forcing. We develop a global simulation
of the UVAI using the 3-D chemical transport model GEOS-Chem coupled with
the Vector Linearized Discrete Ordinate Radiative Transfer model (VLIDORT).
The simulation is applied to interpret UVAI observations from the Ozone
Monitoring Instrument (OMI) for the year 2007. Simulated and observed values
are highly consistent in regions where mineral dust dominates the UVAI, but
a large negative bias (−0.32 to −0.97) exists between simulated and observed
values in biomass burning regions. We determine effective optical properties
for absorbing organic aerosol, known as brown carbon (BrC), and implement
them into GEOS-Chem to better represent observed UVAI values over biomass
burning regions. The inclusion of absorbing BrC decreases the mean bias
between simulated and OMI UVAI values from −0.57 to −0.09 over West Africa
in January, from −0.32 to +0.0002 over South Asia in April, from −0.97 to
−0.22 over southern Africa in July, and from −0.50 to +0.33 over South
America in September. The spectral dependence of absorption after including
BrC in the model is broadly consistent with reported observations for
biomass burning aerosol, with absorbing Ångström exponent (AAE) values
ranging from 2.9 in the ultraviolet (UV) to 1.3 across the UV–Near IR
spectrum. We assess the effect of the additional UV absorption by BrC on
atmospheric photochemistry by examining tropospheric hydroxyl radical (OH)
concentrations in GEOS-Chem. The inclusion of BrC decreases OH by up to
30 % over South America in September, up to 20 % over southern Africa in
July, and up to 15 % over other biomass burning regions. Global annual
mean OH concentrations in GEOS-Chem decrease due to the presence of
absorbing BrC, increasing the methyl chloroform lifetime from 5.62 to
5.68 years, thus reducing the bias against observed values. We calculate the
direct radiative effect (DRE) of BrC using GEOS-Chem coupled with the
radiative transfer model RRTMG (GC-RT). Treating organic aerosol as
containing more strongly absorbing BrC changes the global annual mean
all-sky top of atmosphere (TOA) DRE by +0.03 W m<sup>−2</sup> and all-sky
surface DRE by −0.08 W m<sup>−2</sup>. Regional changes of up to +0.3 W m<sup>−2</sup> at TOA and down to −1.5 W m<sup>−2</sup> at the surface are found over major
biomass burning regions. |
url |
https://www.atmos-chem-phys.net/16/2507/2016/acp-16-2507-2016.pdf |
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