Reactive nitrogen around the Arabian Peninsula and in the Mediterranean Sea during the 2017 AQABA ship campaign

Friedrich, Nils; Eger, Philipp; Shenolikar, Justin; Sobanski, Nicolas; Schuladen, Jan; Dienhart, Dirk; Hottmann, Bettina; Tadic, Ivan; Fischer, Horst; Martinez, Monica; Rohloff, Roland; Tauer, Sebastian; Harder, Hartwig; Pfannerstill, Eva Y.; Wang, Nijing; Williams, Jonathan; Brooks, James; Drewnick, Frank; Su, Hang; Li, Guo; Cheng, Yafang; Lelieveld, Jos; Crowley, John N.

We present shipborne measurements of NOinline-formulax (inline-formula≡ NO inline-formula+ NOinline-formula2) and NOinline-formulay (inline-formula≡ NOinline-formulax+ gas- and particle-phase organic and inorganic oxides of nitrogen) in summer 2017 as part of the expedition “Air Quality and climate change in the Arabian BAsin” (AQABA). The NOinline-formulax and NOinline-formulaz (inline-formula≡ NOinline-formulay-NOinline-formulax) measurements, made with a thermal dissociation cavity ring-down spectrometer (TD-CRDS), were used to examine the chemical mechanisms involved in the processing of primary NOinline-formulax emissions and their influence on the NOinline-formulay budget in chemically distinct marine environments, including the Mediterranean Sea, the Red Sea, and the Arabian Gulf, which were influenced to varying extents by emissions from shipping and oil and gas production. Complementing the TD-CRDS measurements, NO and NOinline-formula2 data sets from a chemiluminescence detector (CLD) were used in the analysis. In all regions, we find that NOinline-formulax is strongly connected to ship emissions, both via direct emission of NO and via the formation of HONO and its subsequent photolytic conversion to NO. The role of HONO was assessed by calculating the NOinline-formulax production rate from its photolysis. Mean NOinline-formula2 lifetimes were 3.9 h in the Mediterranean Sea, 4.0 h in the Arabian Gulf, and 5.0 h in the Red Sea area. The cumulative loss of NOinline-formula2 during the night (reaction with Oinline-formula3) was more important than daytime losses (reaction with OH) over the Arabian Gulf (by a factor 2.8) and over the Red Sea (factor 2.9), whereas over the Mediterranean Sea, where OH levels were high, daytime losses dominated (factor 2.5). Regional ozone production efficiencies (OPEs; calculated from the correlation between Oinline-formulax and NOinline-formulaz, where Oinline-formulax= Oinline-formula3+ NOinline-formula2) ranged from 10.5 inline-formula± 0.9 to 19.1 inline-formula± 1.1. This metric quantifies the relative strength of photochemical Oinline-formula3 production from NOinline-formulax compared to the competing sequestering into NOinline-formulaz species. The largest values were found over the Arabian Gulf, consistent with high levels of Oinline-formula3 found in that region (10–90 percentiles range: 23–108 ppbv). The fractional contribution of individual NOinline-formulaz species to NOinline-formulay exhibited a large regional variability, with HNOinline-formula3 generally the dominant component (on average 33 % of NOinline-formulay) with significant contributions from organic nitrates (11 %) and particulate nitrates in the PMinline-formula1 size range (8 %).

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Friedrich, Nils / Eger, Philipp / Shenolikar, Justin / et al: Reactive nitrogen around the Arabian Peninsula and in the Mediterranean Sea during the 2017 AQABA ship campaign. 2021. Copernicus Publications.

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