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Measurement report: Nitrogen isotopes (δ15N) and first quantification of oxygen isotope anomalies (Δ17O, δ18O) in atmospheric nitrogen dioxide

Sarah Albertin 1, 2 Joël Savarino 1 Slimane Bekki 2 Albane Barbero 1 Nicolas Caillon 1
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : The isotopic composition of nitrogen and oxygen in nitrogen dioxide (NO2) potentially carries a wealth of information about the dynamics of the nitrogen oxides (NOx = nitric oxide(NO) + NO2) chemistry in the atmosphere. While nitrogen isotopes of NO2 are subtle indicators of emissions, NOx chemistry and isotopic nitrogen exchange between NO and NO2, oxygen isotopes are believed to reflect only the O3/NOx/VOC chemical regime in different atmospheric environments. In order to access this potential tracer of the tropospheric chemistry, we have developed an efficient active method to trap atmospheric NO2 on denuder tubes and measured, for the first time, its multi-isotopic composition (δ15N, δ18O, and Δ17O). The δ15N values of NO2 trapped at our site in Grenoble, France, show little variability (−11.8 to −4.9 ‰) with negligible N isotope fractionations between NO and NO2 due to high NO2/NOx ratios. NOx emissions main sources are estimated using a stable isotope model indicating the predominance of traffic NOx emissions in this area. The Δ17O values, however, reveal an important diurnal cycle peaking in late morning at (39.2 ± 1.7) ‰ and decreasing at night until (20.5 ± 1.7) ‰. On top of this diurnal cycle, Δ17O also has substantial variability during the day (from 29.7 to 39.2 ‰), certainly driven by changes in the O3 to peroxyl radicals ratio. The night-time decay of Δ17O(NO2) appears to be driven by NO2 slow removal, mostly from conversion into N2O5, and its formation from the reaction between O3 and emitted NO. Our Δ17O(NO2) measured towards the end of the night is quantitatively consistent with typical values of Δ17O(O3). These preliminary results are very promising for using Δ17O of NO2 as a probe of the atmospheric oxidative activity and for interpreting NO3− isotopic composition records.
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Submitted on : Tuesday, December 15, 2020 - 11:29:20 AM
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Sarah Albertin, Joël Savarino, Slimane Bekki, Albane Barbero, Nicolas Caillon. Measurement report: Nitrogen isotopes (δ15N) and first quantification of oxygen isotope anomalies (Δ17O, δ18O) in atmospheric nitrogen dioxide. Atmospheric Chemistry and Physics Discussions, European Geosciences Union, 2020, pp.(Under Review). ⟨10.5194/acp-2020-1143⟩. ⟨insu-03066334⟩



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