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

The isotopic composition of nitrogen and oxygen in nitrogen dioxide (NOinline-formula2) potentially carries a wealth of information about the dynamics of the nitrogen oxides (NOinline-formulaxinline-formula= nitric oxide (NO) inline-formula+ NOinline-formula2) chemistry in the atmosphere. While nitrogen isotopes of NOinline-formula2 are subtle indicators of NOinline-formulax emissions and chemistry, oxygen isotopes are believed to reflect only the Oinline-formula3inline-formula $M12inlinescrollmathml/$ 8pt14ptsvg-formulamathimg6bfc4ae3491d603d986b6e1d0e6866cf acp-21-10477-2021-ie00001.svg8pt14ptacp-21-10477-2021-ie00001.png  NOinline-formulaxinline-formula $M14inlinescrollmathml/$ 8pt14ptsvg-formulamathimg539a58614ea8688159b8effbc6d3da8d acp-21-10477-2021-ie00002.svg8pt14ptacp-21-10477-2021-ie00002.png  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 NOinline-formula2 on denuder tubes and measured, for the first time, its multi-isotopic composition (inline-formulaδ15N, inline-formulaδ18O, and inline-formulaΔ17O). The inline-formulaΔ17O values of NOinline-formula2 trapped at our site in Grenoble, France, show a large diurnal cycle peaking in late morning at (39.2 inline-formula± 0.3) ‰ and decreasing at night until (20.5 inline-formula± 0.3) ‰. On top of this diurnal cycle, inline-formulaΔ17O also exhibits substantial daytime variability (from 29.7 ‰ to 39.2 ‰), certainly driven by changes in the Oinline-formula3 to peroxyl radicals (ROinline-formula2) ratio. The nighttime decay of inline-formulaΔ17O(NOinline-formula2) appears to be driven by NOinline-formula2 slow removal, mostly from conversion into Ninline-formula2Oinline-formula5, and its formation from the reaction between Oinline-formula3 and freshly emitted NO. As expected from a nighttime inline-formulaΔ17O(NOinline-formula2) expression, our inline-formulaΔ17O(NOinline-formula2) measured towards the end of the night is quantitatively consistent with typical values of inline-formulaΔ17O(Oinline-formula3). Daytime N isotope fractionation is estimated using a general expression linking it to inline-formulaΔ17O(NOinline-formula2). An expression is also derived for the nighttime N isotope fractionation. In contrast to inline-formulaΔ17O(NOinline-formula2), inline-formulaδ15N(NOinline-formula2) measurements exhibit little diurnal variability (inline-formula−11.8 ‰ to inline-formula−4.9 ‰) with negligible isotope fractionations between NO and NOinline-formula2, mainly due to high NOinline-formula2inline-formula $M48inlinescrollmathml/$ 8pt14ptsvg-formulamathimgc435aaf3008f447f555024ce6ff0eeff acp-21-10477-2021-ie00003.svg8pt14ptacp-21-10477-2021-ie00003.png  NOinline-formulax ratios, excepted during the morning rush hours. The main NOinline-formulax emission sources are estimated using a Bayesian isotope mixing model, indicating the predominance of traffic emissions in this area. These preliminary results are very promising for using the combination of inline-formulaΔ17O and inline-formulaδ15N of NOinline-formula2 as a probe of the NOinline-formulax sources and fate and for interpreting nitrate isotopic composition records.

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Albertin, Sarah / Savarino, Joël / Bekki, Slimane / et al: Measurement report: Nitrogen isotopes (δ15N) and first quantification of oxygen isotope anomalies (Δ17O, δ18O) in atmospheric nitrogen dioxide. 2021. Copernicus Publications.

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