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Reactive nitrogen around the Arabian Peninsula and in the Mediterranean Sea during the 2017 AQABA ship campaign
We present shipborne measurements of NOx (≡ NO + NO2) and NOy (≡ NOx+ 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 NOx and NOz (≡ NOy-NOx) measurements, made with a therma...
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Published in: | Atmospheric chemistry and physics 2021-05, Vol.21 (10), p.7473-7498 |
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Main Authors: | , , , , , , , , , , , , , , , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
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Summary: | We present shipborne measurements of NOx (≡ NO + NO2) and NOy (≡ NOx+ 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 NOx and NOz (≡ NOy-NOx)
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 NOx emissions and their influence on the NOy
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 NO2 data sets from a
chemiluminescence detector (CLD) were used in the analysis. In all regions,
we find that NOx 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 NOx production rate from its photolysis. Mean NO2 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 NO2 during the
night (reaction with O3) 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 Ox and
NOz, where Ox= O3+ NO2) ranged from 10.5 ± 0.9 to 19.1 ± 1.1. This metric quantifies the relative strength of
photochemical O3 production from NOx compared to the competing
sequestering into NOz species. The largest values were found over the
Arabian Gulf, consistent with high levels of O3 found in that region
(10–90 percentiles range: 23–108 ppbv). The fractional contribution of
individual NOz species to NOy exhibited a large regional
variability, with HNO3 generally the dominant component (on average
33 % of NOy) with significant contributions from organic nitrates
(11 %) and particulate nitrates in the PM1 size range (8 %). |
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ISSN: | 1680-7324 1680-7316 1680-7324 |
DOI: | 10.5194/acp-21-7473-2021 |