In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 19, No. 6 ( 2019-03-29), p. 3981-4003
Abstract:
Abstract. We present a comprehensive simulation of tropospheric chlorine
within the GEOS-Chem global 3-D model of oxidant–aerosol–halogen atmospheric
chemistry. The simulation includes explicit accounting of chloride
mobilization from sea salt aerosol by acid displacement of HCl and by other
heterogeneous processes. Additional small sources of tropospheric chlorine
(combustion, organochlorines, transport from stratosphere) are also included.
Reactive gas-phase chlorine Cl*, including Cl, ClO, Cl2, BrCl, ICl,
HOCl, ClNO3, ClNO2, and minor species, is produced by the
HCl+OH reaction and by heterogeneous conversion of sea salt aerosol
chloride to BrCl, ClNO2, Cl2, and ICl. The model
successfully simulates the observed mixing ratios of HCl in marine air
(highest at northern midlatitudes) and the associated HNO3
decrease from acid displacement. It captures the high ClNO2 mixing
ratios observed in continental surface air at night and attributes the
chlorine to HCl volatilized from sea salt aerosol and transported inland
following uptake by fine aerosol. The model successfully simulates the
vertical profiles of HCl measured from aircraft, where enhancements in the
continental boundary layer can again be largely explained by transport inland
of the marine source. It does not reproduce the boundary layer Cl2
mixing ratios measured in the WINTER aircraft campaign (1–5 ppt in the
daytime, low at night); the model is too high at night, which could be due to
uncertainty in the rate of the ClNO2+Cl- reaction, but we have
no explanation for the high observed Cl2 in daytime. The global
mean tropospheric concentration of Cl atoms in the model is 620 cm−3
and contributes 1.0 % of the global oxidation of methane, 20 % of
ethane, 14 % of propane, and 4 % of methanol. Chlorine chemistry
increases global mean tropospheric BrO by 85 %, mainly through the
HOBr+Cl- reaction, and decreases global burdens of tropospheric
ozone by 7 % and OH by 3 % through the associated bromine radical
chemistry. ClNO2 chemistry drives increases in ozone of up to
8 ppb over polluted continents in winter.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-19-3981-2019
DOI:
10.5194/acp-19-3981-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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