In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 21, No. 22 ( 2021-11-23), p. 16955-16984
Abstract:
Abstract. This paper presents a modelling study on the fate of CHBr3 and its
product gases in the troposphere within the context of tropical deep
convection. A cloud-scale case study was conducted along the west coast of
Borneo, where several deep convective systems were triggered on the afternoon and
early evening of 19 November 2011. These systems were sampled by the Falcon
aircraft during the field campaign of the SHIVA project and analysed using a
simulation with the cloud-resolving meteorological model C-CATT-BRAMS at 2×2 km resolution that represents the emissions, transport by
large-scale flow, convection, photochemistry, and washout of CHBr3
and its product gases (PGs). We find that simulated CHBr3 mixing
ratios and the observed values in the boundary layer and the outflow of the
convective systems agree. However, the model underestimates the background
CHBr3 mixing ratios in the upper troposphere, which suggests a
missing source at the regional scale. An analysis of the simulated chemical
speciation of bromine within and around each simulated convective system
during the mature convective stage reveals that 〉85 % of the
bromine derived from CHBr3 and its PGs is transported vertically to
the point of convective detrainment in the form of CHBr3 and that
the remaining small fraction is in the form of organic PGs, principally
insoluble brominated carbonyls produced from the photo-oxidation of
CHBr3. The model simulates that within the boundary layer and free
troposphere, the inorganic PGs are only present in soluble forms, i.e. HBr,
HOBr, and BrONO2, and, consequently, within the convective clouds,
the inorganic PGs are almost entirely removed by wet scavenging. We find that
HBr is the most abundant PG in background lower-tropospheric air and that this
prevalence of HBr is a result of the relatively low background tropospheric
ozone levels at the regional scale. Contrary to a previous study in a
different environment, for the conditions in the simulation, the insoluble
Br2 species is hardly formed within the convective systems and
therefore plays no significant role in the vertical transport of bromine. This
likely results from the relatively small quantities of simulated inorganic
bromine involved, the presence of HBr in large excess compared to HOBr and
BrO, and the relatively efficient removal of soluble compounds within the
convective column.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-21-16955-2021
DOI:
10.5194/acp-21-16955-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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