Non-methane hydrocarbon (C<sub>2</sub>–C<sub>8</sub>) sources and sinks around the Arabian Peninsula
<p>Atmospheric non-methane hydrocarbons (NMHCs) have been extensively studied around the globe due to their importance to atmospheric chemistry and their utility in emission source and chemical sink identification. This study reports on shipborne NMHC measurements made around the Arabian Penin...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-05-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/7209/2019/acp-19-7209-2019.pdf |
| Summary: | <p>Atmospheric
non-methane hydrocarbons (NMHCs) have been extensively studied around the
globe due to their importance to atmospheric chemistry and their utility in
emission source and chemical sink identification. This study reports on
shipborne NMHC measurements made around the Arabian Peninsula during the
AQABA (Air Quality and climate change in the Arabian BAsin) ship campaign.
The ship traversed the Mediterranean Sea, the Suez Canal, the Red Sea, the
northern Indian Ocean, and the Arabian Gulf, before returning by the same
route. The Middle East is one of the largest producers of oil and gas
(O&G), yet it is among the least studied. Atmospheric mixing ratios of
<span class="inline-formula">C<sub>2</sub></span>–<span class="inline-formula">C<sub>8</sub></span> hydrocarbons ranged from a few ppt in unpolluted
regions (Arabian Sea) to several ppb over the Suez Canal and Arabian Gulf
(also known as the Persian Gulf), where a maximum of 166.5 ppb of alkanes
was detected. The ratio between <span class="inline-formula"><i>i</i></span>-pentane and <span class="inline-formula"><i>n</i></span>-pentane was found to be
<span class="inline-formula">0.93±0.03</span> ppb ppb<span class="inline-formula"><sup>−1</sup></span> over the Arabian Gulf, which is indicative
of widespread O&G activities, while it was <span class="inline-formula">1.71±0.06</span> ppb ppb<span class="inline-formula"><sup>−1</sup></span> in the Suez Canal, which is a characteristic signature
of ship emissions. We provide evidence that international shipping
contributes to ambient <span class="inline-formula">C<sub>3</sub></span>–<span class="inline-formula">C<sub>8</sub></span> hydrocarbon concentrations but
not to ethane, which was not detected in marine traffic exhausts. NMHC
relationships with propane differentiated between alkane-rich associated gas
and methane-rich non-associated gas through a characteristic enrichment of
ethane over propane atmospheric mixing ratios. Utilizing the
variability–lifetime relationship, we show that atmospheric chemistry
governs the variability of the alkanes only weakly in the source-dominated
areas of the Arabian Gulf (<span class="inline-formula"><i>b</i><sub>AG</sub>=0.16</span>) and along the northern part
of the Red Sea (<span class="inline-formula"><i>b</i><sub>RSN</sub>=0.22</span>), but stronger dependencies are found in
unpolluted regions such as the Gulf of Aden (<span class="inline-formula"><i>b</i><sub>GA</sub>=0.58</span>) and the
Mediterranean Sea (<span class="inline-formula"><i>b</i><sub>MS</sub>=0.48</span>). NMHC oxidative pair analysis
indicated that OH chemistry dominates the oxidation of hydrocarbons in the
region, but along the Red Sea and the Arabian Gulf the NMHC ratios
occasionally provided evidence of chlorine radical chemistry. These results
demonstrate the utility of NMHCs as source/sink identification tracers and
provide an overview of NMHCs around the Arabian Peninsula.</p> |
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| ISSN: | 1680-7316 1680-7324 |