Global and Regional Decreases in Tropospheric Oxidants From Photochemical
Effects of Aerosols
Randall V. Martin, Daniel J. Jacob, Robert M. Yantosca, Mian Chin,
and, Paul Ginoux
J. Geophys. Res., 108(D3), 4097, doi:10.1029/2002JD002622, 2003.
Abstract
We evaluate the sensitivity of tropospheric OH, O3, and O3 precursors to
photochemical effects of aerosols not usually included in global models:
(1) aerosol scattering and absorption of ultraviolet radiation, and (2) reactive uptake of HO2, NO2, and NO3. Our approach is to couple a global 3-D
model of tropospheric chemistry (GEOS-CHEM) with aerosol fields
from a global 3-D aerosol model (GOCART). Reactive uptake by aerosols is computed using
reaction probabilities from a recent review (gHO2=0.2, gNO2=10-4,
gNO3=10-3). Aerosols decrease the O3->(O1D) photolysis frequency by 5-20% at
the surface throughout the Northern Hemisphere (largely due to mineral dust)
and by a factor of 2 in biomass burning regions (largely due to black
carbon). Aerosol uptake of HO2 accounts for 10-40% of total HOx radical (=OH+peroxy) loss in the boundary layer over polluted continental regions
(largely due to sulfate and organic carbon) and for more than 70% over tropical
biomass burning regions (largely due to organic carbon). Uptake of NO2 and
NO3 accounts for 10-20% of total HNO3 production over biomass burning
regions and less elsewhere. Annual mean OH
concentrations decrease by 9% globally and by 5-35% in the boundary layer
over the Northern Hemisphere. Simulated CO increases by 5-15 ppbv in the
remote Northern Hemisphere, improving
agreement with observations. Simulated boundary-layer O3 decreases by 15-45
ppbv over India during the biomass burning season in March, and by 5-9 ppbv
over northern Europe in August, again improving comparison with observations.
We find that particulate matter controls would increase surface O3 over Europe and other
industrial regions.
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