Preprints
https://doi.org/10.5194/acp-2021-487
https://doi.org/10.5194/acp-2021-487

  19 Jul 2021

19 Jul 2021

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

Oxidation pathways and emission sources of atmospheric particulate nitrate in Seoul: based on δ15N and Δ 17O of PM2.5

Saehee Lim1, Meehye Lee1, Joel Savarino2, and Paolo Laj2 Saehee Lim et al.
  • 1Dept. of Earth and Environmental Sciences, Korea University, Seoul, 02841, South Korea
  • 2Univ. Grenoble-Alpes, CNRS, IRD, Grenoble INP, Institute for Geosciences and Environmental Research (IGE), Grenoble, 38000, France

Abstract. PM2.5 haze pollution driven by secondary inorganic NO3 has been a great concern in East Asia. It is, therefore, imperative to identify its sources and oxidation processes, for which nitrogen and oxygen stable isotopes are powerful tracers. Here, we determined the δ15N (NO3) and Δ17O (NO3) of PM2.5 in Seoul from 2018 to 2019, and estimated quantitatively the relative contribution of oxidation pathways for particulate NO3 and major NOx emission sources. In the range of PM2.5 mass concentration from 7.5 g m−3 (summer) to 139.0 g m−3 (winter), the mean δ15N was −0.7 ± 3.3 ‰ and 3.8 ± 3.7 ‰, and the mean Δ17O was 23.2 ± 2.2 ‰ and 27.7 ± 2.2 ‰ in the summer and winter, respectively. While OH oxidation was the dominant pathway for NO3 during the summer (87 %), nighttime formation via N2O5 and NO3 was more important (38 %) during the winter, when aerosol liquid water content (AWLC) and nitrogen oxidation ratio (NOR) were higher. Interestingly, the highest Δ17O was coupled with the lowest δ 15N and highest NOR in record-breaking winter PM2.5 episodes, revealing the critical role of photochemical oxidation process in severe winter haze development. For NOx sources, vehicle emissions were confirmed as a main contributor, followed by biomass combustion from various activities. The contribution from biogenic soil and coal combustion was slightly increased in summer and winter, respectively. Our results built on multiple-isotope approach provide the first explicit evidence for NO3 formation processes and major NOx emission sources in Seoul megacity and suggest an effective mitigation measure to improve PM2.5 pollution.

Saehee Lim et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-487', Anonymous Referee #1, 15 Aug 2021
  • RC2: 'Comment on acp-2021-487', Anonymous Referee #2, 30 Sep 2021

Saehee Lim et al.

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Short summary
We determined δ15N(NO3) and Δ17O(NO3) of PM2.5 in Seoul during 2018–2019, and estimated quantitatively the contribution of oxidation pathways for NO3 and NOx emission sources. The nighttime pathway played a significant role in NO3 formation during the winter and its contribution further increased up to 70 % on haze days with PM2.5 > 75 g m−3. The vehicle emissions were confirmed as main NO3 source, followed by biomass combustion, which is not considered a NOx source in emission inventories.
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