Preprints
https://doi.org/10.5194/acp-2020-1143
https://doi.org/10.5194/acp-2020-1143

  14 Dec 2020

14 Dec 2020

Review status: this preprint is currently under review for the journal ACP.

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

Sarah Albertin1,2, Joël Savarino2, Slimane Bekki1, Albane Barbero2, and Nicolas Caillon2 Sarah Albertin et al.
  • 1LATMOS/IPSL, Sorbonne Université, UVSQ, CNRS, 75005 Paris, France
  • 2IGE, Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, 38000 Grenoble, France

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.

Sarah Albertin et al.

 
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Sarah Albertin et al.

Sarah Albertin et al.

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Short summary
We report an efficient method to collect atmospheric NO2 adapted for isotopic analysis and present the first measurements of NO2 triple oxygen isotopes and double nitrogen isotopes. Atmospheric samplings carried out in Grenoble, France, highlight the sensitivity of NO2 isotopic signatures to the local NOx emissions and chemical regimes. The quantification of the NO2 oxygen isotope anomaly opens new perspectives in the study of the NOx oxidation pathways to nitrate.
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