Cloud-scale modelling of the impact of deep convection on the fate of oceanic bromoform in the troposphere: a case study over the west coast of Borneo
<p>This paper presents a modelling study on the fate of <span class="inline-formula">CHBr<sub>3</sub></span> 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...
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| Autores principales: | , , , , , , , , , , , , , , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
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Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/9a7cab26655a4e25a000fdd477159eae |
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| Sumario: | <p>This paper presents a modelling study on the fate of <span class="inline-formula">CHBr<sub>3</sub></span> 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 <span class="inline-formula">2×2</span> <span class="inline-formula">km</span> resolution that represents the emissions, transport by
large-scale flow, convection, photochemistry, and washout of <span class="inline-formula">CHBr<sub>3</sub></span>
and its product gases (PGs). We find that simulated <span class="inline-formula">CHBr<sub>3</sub></span> mixing
ratios and the observed values in the boundary layer and the outflow of the
convective systems agree. However, the model underestimates the background
<span class="inline-formula">CHBr<sub>3</sub></span> 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 <span class="inline-formula">>85</span> <span class="inline-formula">%</span> of the
bromine derived from <span class="inline-formula">CHBr<sub>3</sub></span> and its PGs is transported vertically to
the point of convective detrainment in the form of <span class="inline-formula">CHBr<sub>3</sub></span> and that
the remaining small fraction is in the form of organic PGs, principally
insoluble brominated carbonyls produced from the photo-oxidation of
<span class="inline-formula">CHBr<sub>3</sub></span>. The model simulates that within the boundary layer<span id="page16956"/> and free
troposphere, the inorganic PGs are only present in soluble forms, i.e. HBr,
HOBr, and <span class="inline-formula">BrONO<sub>2</sub></span>, 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
<span class="inline-formula">Br<sub>2</sub></span> 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.</p> |
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