EGU21-2634, updated on 03 Nov 2023
https://doi.org/10.5194/egusphere-egu21-2634
EGU General Assembly 2021
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Nitrogen isotopes (δ15N) and oxygen isotope anomalies (Δ17O, δ18O) in atmospheric nitrogen dioxide : a new perspective for isotopic constraints on oxidation and aerosols formation processes

Sarah Albertin1,2, Slimane Bekki1, and Joël Savarino2
Sarah Albertin et al.
  • 1LATMOS/IPSL, Sorbonne Université, UVSQ, CNRS, 75005 Paris, France (sarah.albertin@latmos.ipsl.fr)
  • 2IGE, Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, 38000 Grenoble, France

Urban polar areas can be subject to severe pollution in winter, linked to sharp temperature inversions that trap pollutants close to the surface. However, the formation of secondary aerosols (sulphates, nitrates, organics) in these cold and dark conditions and the role of the Arctic boundary layer are still poorly understood. To address this issue, an intensive international measurement campaign, called ALPACA (ALaskan Pollution And Chemical Analysis), will be conducted in January/February 2021 in and around Fairbanks, Alaska. Among the various atmospheric chemical and physical measurements, gas and particles collections will be carried out for multiple isotopic analyses.

The use of stable isotopes over the past decades has demonstrated its ability to provide information relevant for tracing emission sources, individual chemical processes and budgets of atmospheric trace gases. Of particular interest is the propagation of the ozone distinctive oxygen-17 anomaly (Δ17O) into the reactive nitrogen cycle which has led to a better understanding of nitrate formation pathways in various environments. However, there remain some difficulties to interpret the isotopic composition of the nitrate, mainly due to the lack of clearly established understanding about the link between the oxygen and nitrogen isotopic composition of the nitrogen oxides (NOx = NO + NO2), the precursors of nitrate in the atmosphere, and the chemical state of the atmosphere.

In order to interpret more quantitatively the fate of reactive nitrogen using isotopic records, we have developed an effective active method to trap atmospheric NO2 on denuder tubes and have 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 isotopefractionations during the NO and NO2 interconversion due to high NO2/NOx ratios. The main sources of NOx emissions are estimated using a stable isotope model applied to our δ15N measurements; the results indicate the predominance of traffic NOx emissions in this area. The Δ17O values exhibit an important diurnal cycle with a late morning peak at (39.2 ± 1.7) ‰ and a night-time decrease with a late-night minimum at (20.5 ± 1.7) ‰. On top of this general diurnal cycle,  Δ17O also shows 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 slow removal of NO2, mostly from its conversion into N2O5, and its formation from the reaction between O3 and emitted NO. As expected, our Δ17O(NO2) values measured towards the end of the night are quantitatively consistent with typical values of Δ17O(O3).

These preliminary results are very promising for the use of Δ17O of NO2 as a probe of the atmospheric oxidative activity and for the interpretation of  NO3- isotopic composition records. In the future, samplings and multi-isotopic analysis of atmospheric nitrate performed in parallel with those of NO2 will be of great interest for the study of the full reactive nitrogen cycle.

How to cite: Albertin, S., Bekki, S., and Savarino, J.: Nitrogen isotopes (δ15N) and oxygen isotope anomalies (Δ17O, δ18O) in atmospheric nitrogen dioxide : a new perspective for isotopic constraints on oxidation and aerosols formation processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2634, https://doi.org/10.5194/egusphere-egu21-2634, 2021.

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