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

MPS-Authors
/persons/resource/persons207351

Pfannerstill,  Eva Y.
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons239555

Wang,  Nijing
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons207353

Edtbauer,  Achim
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons100860

Bourtsoukidis,  Efstratios
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons239557

Dienhart,  Dirk
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons230536

Eger,  Philipp G.
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons211374

Ernle,  Lisa
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons100935

Fischer,  Horst
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons204321

Hottmann,  Bettina
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons195368

Stönner,  Christof
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons192706

Tadic,  Ivan
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons127609

Walter,  David
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

/persons/resource/persons101364

Williams,  J.
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Citation

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.


Cite as: http://hdl.handle.net/21.11116/0000-0004-CD73-4
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.