Characterization of Carbonyl Compounds Measured by PTR-Tof-MS around Arabian Peninsula (AQABA Ship Campaign)

From June to August 2017, a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) was operated on board the research vessel Kommandor Iona during the AQABA (Air Quality and Climate Change in the Arabian Basin) ship campaign to measure volatile organic compounds (VOCs) continuously in the marine atmospheric boundary layer around the Arabian Peninsula. Air quality in this region is heavily influenced by emissions from marine transportation and the oil/petroleum industry, strong photochemistry (due to high sunlight and moisture levels) and dust. Carbonyl compounds (CCs, C_xH_yO), are important intermediates in the atmospheric oxidation of VOCs. This study focusses on their regional distribution, photochemical source strengths, OH reactivity contribution, and relative abundance of CCs to better understand the air chemistry in the region. For aliphatic CCs (C1-C9), acetone had the highest mixing ratio among most of the regions varying from 0.45 ppb in Arabian Sea to 4.5 ppb in the Arabian Gulf, followed by formaldehyde (measured by Hantzsch monitor), acetaldehyde and C4-C9 CCs. Aliphatic CCs correlated well among each other (r² > 0.7) in the Arabian Gulf, suggesting that air oxidation was dominated by local oxidation process. It also explained that the extremely high ozone (above 100 ppb) observed in this area was driven by VOCs (r² > 0.5 between aliphatic CCs and ozone). Model comparison showed that acetaldehyde was underestimated in most of the area, indicating the existence of additional source processes. Unsaturated CCs (C4-C9) varied from 10 to 650 ppt during the campaign and were found at relatively low levels compared with C4-C9 aliphatic CCs (10 ppt - 12 ppb). Nonetheless, the unsaturated CCs could contribute more to OH reactivity. This unique dataset obtained from the campaign can provide new insights into the atmospheric processes in the Middle East, to assess the impact of the oil industry related emissions and improve the model predictions related to air quality in that region.