Novel approaches to improve estimates of short-lived halocarbon emissions during summer from the Southern Ocean using airborne observations
<p>Fluxes of halogenated volatile organic compounds (VOCs) over the Southern Ocean remain poorly understood, and few atmospheric measurements exist to constrain modeled emissions of these compounds. We present observations of <span class="inline-formula">CHBr<sub>3</su...
Main Authors: | , , , , , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2019-11-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/19/14071/2019/acp-19-14071-2019.pdf |
Summary: | <p>Fluxes of halogenated volatile organic compounds (VOCs) over the Southern
Ocean remain poorly understood, and few atmospheric measurements exist to
constrain modeled emissions of these compounds. We present observations of
<span class="inline-formula">CHBr<sub>3</sub></span>, <span class="inline-formula">CH<sub>2</sub>Br<sub>2</sub></span>, <span class="inline-formula">CH<sub>3</sub>I</span>, <span class="inline-formula">CHClBr<sub>2</sub></span>, <span class="inline-formula">CHBrCl<sub>2</sub></span>, and
<span class="inline-formula">CH<sub>3</sub>Br</span> during the <span class="inline-formula">O<sub>2</sub>∕N<sub>2</sub></span> Ratio and <span class="inline-formula">CO<sub>2</sub></span> Airborne Southern
Ocean (ORCAS) study and the second Atmospheric Tomography mission
(ATom-2) in January and February of 2016 and 2017. Good model–measurement
correlations were obtained between these observations and simulations from
the Community Earth System Model (CESM) atmospheric component with chemistry
(CAM-Chem) for <span class="inline-formula">CHBr<sub>3</sub></span>, <span class="inline-formula">CH<sub>2</sub>Br<sub>2</sub></span>, <span class="inline-formula">CH<sub>3</sub>I</span>, and <span class="inline-formula">CHClBr<sub>2</sub></span> but
all showed significant differences in model : measurement ratios. The
model : measurement comparison for <span class="inline-formula">CH<sub>3</sub>Br</span> was satisfactory and for
<span class="inline-formula">CHBrCl<sub>2</sub></span> the low levels present precluded us from making a complete
assessment. Thereafter, we demonstrate two novel approaches to estimate
halogenated VOC fluxes; the first approach takes advantage of the robust
relationships that were found between airborne observations of <span class="inline-formula">O<sub>2</sub></span> and
<span class="inline-formula">CHBr<sub>3</sub></span>, <span class="inline-formula">CH<sub>2</sub>Br<sub>2</sub></span>, and <span class="inline-formula">CHClBr<sub>2</sub></span>. We use these linear
regressions with <span class="inline-formula">O<sub>2</sub></span> and modeled <span class="inline-formula">O<sub>2</sub></span> distributions to infer a
biological flux of halogenated VOCs. The second approach uses the Stochastic
Time-Inverted Lagrangian Transport (STILT) particle dispersion model to
explore the relationships between observed mixing ratios and the product of
the upstream surface influence of sea ice, chl <span class="inline-formula"><i>a</i></span>, absorption due to
detritus, and downward shortwave radiation at the surface, which in turn
relate to various regional hypothesized sources of halogenated VOCs such as
marine phytoplankton, phytoplankton in sea-ice brines, and decomposing
organic matter in surface seawater. These relationships can help evaluate
the likelihood of particular halogenated VOC sources and in the case of
statistically significant correlations, such as was found for <span class="inline-formula">CH<sub>3</sub>I</span>, may
be used to derive an estimated flux field. Our results are consistent with a
biogenic regional source of <span class="inline-formula">CHBr<sub>3</sub></span> and both nonbiological and
biological sources of <span class="inline-formula">CH<sub>3</sub>I</span> over these regions.</p> |
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ISSN: | 1680-7316 1680-7324 |