Nitrate chemistry in the northeast US – Part 2: Oxygen isotopes reveal differences in particulate and gas-phase formation

Abstract Δ 17 O) and δ 18 O)) for nitric acid (HNO3) and particulate nitrate (pNO3) from three US EPA Clean Air Status and Trends Network (CASTNET) sites in the northeastern US from December 2016 to 2018. The Δ 17 O, HNO3) and δ 18 O, HNO3) values ranged from 12.9 ‰ to 30.9 ‰ and from 46.9 ‰ to 82.1 ‰, and the Δ 17 O, pNO3) and δ 18 O, pNO3) ranged from 16.6 ‰ to 33.7 ‰ and from 43.6 ‰ to 85.3 ‰, respectively. There was distinct seasonality of δ 18 O) and Δ 17 O), with higher values observed during winter compared to during summer, suggesting a shift in O3 to HOx radical chemistry, as expected. Unexpectedly, there was a statistical difference in Δ 17 O) between HNO3 and pNO3, with higher values observed for pNO3 (27.1 ± 3 (22.7 ± δ 18 O) and Δ 17 O). This difference suggests atmospheric nitrate phase-dependent oxidation chemistry that is not predicted in models. Based on the output from GEOS-Chem and both the δ 18 O) and Δ 17 O) observations, we quantify the production pathways of atmospheric nitrate. The model significantly overestimated the heterogeneous N2 O5 hydrolysis production for both HNO3 and pNO3, a finding consistent with observed seasonal changes in δ 18 O) and Δ 17 O) of HNO3 and pNO3, though large uncertainties remain in the quantitative transfer of δ 18 O) from major atmospheric oxidants. This comparison provides important insight into the role of oxidation chemistry in reconciling a commonly observed positive bias for modeled atmospheric nitrate concentrations in the northeastern US.

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch

References and Relationships

• Bibliographic citation: Nitrate chemistry in the northeast US – Part 2: Oxygen isotopes reveal differences in particulate and gas-phase formation ; volume:23 ; number:7 ; year:2023 ; pages:4203-4219 ; extent:17 ; Atmospheric chemistry and physics ; 23, Heft 7 (2023), 4203-4219 (gesamt 17)

Contributors, Places and Time

• Creator: Kim, Heejeong ; Walters, Wendell W. ; Bekker, Claire ; Murray, Lee T. ; Hastings, Meredith G.

Further information

• DOI: 10.5194/acp-23-4203-2023
• URN: urn:nbn:de:101:1-2023041305180307210648
• Rights: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 14.08.2025, 10:49 AM CEST