Volatile organic compounds (VOCs) were measured around the Arabian Peninsula using a research vessel during the AQABA campaign (Air Quality and Climate Change in the Arabian Basin) from June to August 2017. In this study we examine carbonyl compounds, measured by a proton transfer reaction mass spectrometer (PTR-ToF-MS), and present both a regional concentration distribution and a budget assessment for these key atmospheric species. Among the aliphatic carbonyls, acetone had the highest mixing ratios in most of the regions traversed, varying from 0.43 ppb over the Arabian Sea to 4.5 ppb over the Arabian Gulf, followed by formaldehyde (measured by a Hantzsch monitor, 0.82 ppb over the Arabian Sea and 3.8 ppb over the Arabian Gulf) and acetaldehyde (0.13 ppb over the Arabian Sea and 1.7 ppb over the Arabian Gulf). Unsaturated carbonyls (C4–C9) varied from 10 to 700 ppt during the campaign and followed similar regional mixing ratio dependence to aliphatic carbonyls, which were identified as oxidation products of cycloalkanes over polluted areas. We compared the measurements of acetaldehyde, acetone, and methyl ethyl ketone to global chemistry-transport model (ECHAM5/MESSy Atmospheric Chemistry – EMAC) results. A significant discrepancy was found for acetaldehyde, with the model underestimating the measured acetaldehyde mixing ratio by up to an order of magnitude. Implementing a photolytically driven marine source of acetaldehyde significantly improved the agreement between measurements and model, particularly over the remote regions (e.g. Arabian Sea). However, the newly introduced acetaldehyde source was still insufficient to describe the observations over the most polluted regions (Arabian Gulf and Suez), where model underestimation of primary emissions and biomass burning events are possible reasons.
KAUST Repository Item: Exported on 2022-10-06
Acknowledgements: The position of Nijing Wang was funded by the European Commission, H2020 Research Infrastructures (IMPACT (grant no. 674911)).
The article processing charges for this open-access publication were covered by the Max Planck Society. We are grateful for the collaboration with the King Abdullah University of Science and Technology (KAUST), the Kuwait Institute for Scientific Research (KISR), and the Cyprus Institute (CyI) to fulfill the campaign. We would like to thank Captain Pavel Kirzner and the crew for their full support onboard the Kommandor Iona, Hays Ships Ltd. We are grateful for the support from all members involved in the AQABA campaign, especially Hartwig Harder for his general organization onboard the campaign, and Marcel Dorf, Claus Koeppel, Thomas Klüpfel, and Rolf Hofmann for logistical organization and their help with preparation and set-up. We would like to express our gratitude to Ivan Tadic and Philipp Eger for the use of a ship exhaust contamination flag.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.