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<p>Shipborne measurements of nitryl chloride (<span class="inline-formula">ClNO₂</span>), hydrogen chloride (HCl) and sulfur dioxide (<span class="inline-formula">SO₂</span>) were made during the AQABA (Air Quality and climate change in the Arabian BAsin) ship campaign in summer 2017. The dataset includes measurements over the Mediterranean Sea, the Suez Canal, the Red Sea, the Gulf of Aden, the Arabian Sea, the Gulf of Oman, and the Arabian Gulf (also known as Persian Gulf) with observed <span class="inline-formula">ClNO₂</span> mixing ratios ranging from the limit of detection to <span class="inline-formula">≈600</span>&thinsp;pptv. We examined the regional variability in the generation of <span class="inline-formula">ClNO₂</span> via the uptake of dinitrogen pentoxide (<span class="inline-formula">N₂O₅</span>) to Cl-containing aerosol and its importance for Cl atom generation in a marine boundary layer under the (variable) influence of emissions from shipping and the oil industry. The yield of <span class="inline-formula">ClNO₂</span> formation per <span class="inline-formula">NO₃</span> radical generated was generally low (median of <span class="inline-formula">≈1</span>&thinsp;%–5&thinsp;% depending on the region), mainly as a result of gas-phase loss of <span class="inline-formula">NO₃</span> dominating over heterogeneous loss of <span class="inline-formula">N₂O₅</span>, the latter being disfavoured by the high temperatures found throughout the campaign. The contributions of <span class="inline-formula">ClNO₂</span> photolysis and OH-induced HCl oxidation to Cl-radical formation were derived and their relative contributions over the diel cycle compared. The results indicate that over the northern Red Sea, the Gulf of Suez, and the Gulf of Oman the formation of Cl atoms will enhance the oxidation rates of some volatile organic compounds (VOCs), especially in the early morning.</p>