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  Shipborne measurements of total OH reactivity around the Arabian Peninsula and its role in ozone chemistry

Pfannerstill, E. Y., Wang, N., Edtbauer, A., Bourtsoukidis, E., Crowley, J. N., Dienhart, D., et al. (2019). Shipborne measurements of total OH reactivity around the Arabian Peninsula and its role in ozone chemistry. Atmospheric Chemistry and Physics, 19(17), 11501-11523. doi:10.5194/acp-19-11501-2019.

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 Creators:
Pfannerstill, Eva Y.1, Author              
Wang, Nijing1, Author              
Edtbauer, Achim1, Author              
Bourtsoukidis, Efstratios1, Author              
Crowley, John N.2, Author
Dienhart, Dirk1, Author              
Eger, Philipp G.1, Author              
Ernle, Lisa1, Author              
Fischer, Horst1, Author              
Hottmann, Bettina1, Author              
Paris, Jean-Daniel2, Author
Stönner, Christof1, Author              
Tadic, Ivan1, Author              
Walter, David1, Author              
Williams, J.1, Author              
Affiliations:
1Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_1826285              
2external, ou_persistent22              

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 Abstract: The Arabian Peninsula is characterized by high and increasing levels of photochemical air pollution. Strong solar irradiation, high temperatures and large anthropogenic emissions of reactive trace gases result in intense photochem- ical activity, especially during the summer months. However, air chemistry measurements in the region are scarce. In or- der to assess regional pollution sources and oxidation rates, the first ship-based direct measurements of total OH reac- tivity were performed in summer 2017 from a vessel trav- eling around the peninsula during the AQABA (Air Qual- ity and Climate Change in the Arabian Basin) campaign. Total OH reactivity is the total loss frequency of OH rad- icals due to all reactive compounds present in air and de- fines the local lifetime of OH, the most important oxidant in the troposphere. During the AQABA campaign, the total OH reactivity ranged from below the detection limit (5.4 s − 1 ) over the northwestern Indian Ocean (Arabian Sea) to a maxi- mum of 32 . 8 ± 9 . 6 s − 1 over the Arabian Gulf (also known as Persian Gulf) when air originated from large petroleum ex- traction/processing facilities in Iraq and Kuwait. In the pol- luted marine regions, OH reactivity was broadly compara- ble to highly populated urban centers in intensity and com- position. The permanent influence of heavy maritime traffic over the seaways of the Red Sea, Gulf of Aden and Gulf of Oman resulted in median OH sinks of 7.9–8.5 s − 1 . Due to the rapid oxidation of direct volatile organic compound (VOC) emissions, oxygenated volatile organic compounds (OVOCs) were observed to be the main contributor to OH reactivity around the Arabian Peninsula (9 %–35 % by region). Over the Arabian Gulf, alkanes and alkenes from the petroleum ex- traction and processing industry were an important OH sink with ∼ 9 % of total OH reactivity each, whereas NO x and aromatic hydrocarbons ( ∼ 10 % each) played a larger role in the Suez Canal, which is influenced more by ship traffic and urban emissions. We investigated the number and identity of chemical species necessary to explain the total OH sink. Taking into account ∼ 100 individually measured chemical species, the observed total OH reactivity can typically be ac- counted for within the measurement uncertainty (50 %), with 10 dominant trace gases accounting for 20 %–39 % of re- gional total OH reactivity. The chemical regimes causing the intense ozone pollution around the Arabian Peninsula were investigated using total OH reactivity measurements. Ozone vs. OH reactivity relationships were found to be a useful tool for differentiating between ozone titration in fresh emissions and photochemically aged air masses. Our results show that the ratio of NO x - and VOC-attributed OH reactivity was fa- vorable for ozone formation almost all around the Arabian Peninsula, which is due to NO x and VOCs from ship ex- hausts and, often, oil/gas production. Therewith, total OH reactivity measurements help to elucidate the chemical pro- cesses underlying the extreme tropospheric ozone concentra- tions observed in summer over the Arabian Basin.

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Language(s): eng - English
 Dates: 2019
 Publication Status: Published in print
 Pages: -
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 Table of Contents: -
 Rev. Type: -
 Identifiers: ISI: 000485718200001
DOI: 10.5194/acp-19-11501-2019
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Title: Atmospheric Chemistry and Physics
  Abbreviation : ACP
Source Genre: Journal
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Publ. Info: Göttingen : Copernicus Publications
Pages: - Volume / Issue: 19 (17) Sequence Number: - Start / End Page: 11501 - 11523 Identifier: ISSN: 1680-7316
CoNE: https://pure.mpg.de/cone/journals/resource/111030403014016