Preprints
https://doi.org/10.5194/egusphere-2024-3860
https://doi.org/10.5194/egusphere-2024-3860
17 Dec 2024
 | 17 Dec 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Evaluating Nitrogen Oxide and α-pinene Oxidation Chemistry: Insights from Oxygen and Nitrogen Stable Isotopes

Wendell W. Walters, Masayuki Takeuchi, Danielle E. Blum, Gamze Eris, David Tanner, Weiqi Xu, Jean Rivera-Rios, Fobang Liu, Tianchang Xu, Greg Huey, Justin B. Min, Rodney Weber, Nga L. Ng, and Meredith G. Hastings

Abstract. The chemical interaction between nitrogen oxides (NOx = NO + NO2) and α-pinene plays a critical role in air quality and climate. However, uncertainties remain regarding their coupling in NOx loss, renoxification, and oxidation chemistry. To address these gaps, we conducted controlled chamber experiments, analyzing nitric acid (HNO3), NO2, and particulate nitrate (pNO3) for their oxygen and nitrogen stable isotope variations (Δ17O, δ18O, and δ15N). A strong linear relationship between δ18O and Δ17O across experiments revealed contributions of oxygen from ozone (O3) and atmospheric oxygen (O2) in forming reactive radicals. The δ15N values followed the order δ15N(pNO3) < NO2 < HNO3, reflecting isotope fractionation during NOx oxidation. A new chemical mechanism accurately predicted aerosol precursor decay and simulated Δ17O and δ15N values. Simulations showed NOx photochemical cycling and pNO3 formation, primarily from organic nitrate, with Δ17O(NO2) simulations achieving a root mean square error (RMSE) of 1.7 ‰. Improved δ15N(NO2) and pNO3 simulations used a nitrogen isotope fractionation factor (15α) of 0.997 for NO2 + OH reactions. However, modeling Δ17O and δ15N of HNO3 proved challenging, likely due to sampling artifacts. This study provides insights into Δ17O transfer dynamics, nitrogen isotope fractionation, and the role of NOx-BVOC chemistry in air quality, highlighting the potential of Δ17O and δ15N as tools for evaluating complex atmospheric processes.

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Wendell W. Walters, Masayuki Takeuchi, Danielle E. Blum, Gamze Eris, David Tanner, Weiqi Xu, Jean Rivera-Rios, Fobang Liu, Tianchang Xu, Greg Huey, Justin B. Min, Rodney Weber, Nga L. Ng, and Meredith G. Hastings

Status: open (until 28 Jan 2025)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
Wendell W. Walters, Masayuki Takeuchi, Danielle E. Blum, Gamze Eris, David Tanner, Weiqi Xu, Jean Rivera-Rios, Fobang Liu, Tianchang Xu, Greg Huey, Justin B. Min, Rodney Weber, Nga L. Ng, and Meredith G. Hastings

Model code and software

Walters-Research-Group/alpha-pinene_NOx_Chemistry_Box_Model_Simulations: v1.0 alpha-pinene NOx F0AM Box Model Simualtions Wendell Walters https://zenodo.org/records/14241585

Wendell W. Walters, Masayuki Takeuchi, Danielle E. Blum, Gamze Eris, David Tanner, Weiqi Xu, Jean Rivera-Rios, Fobang Liu, Tianchang Xu, Greg Huey, Justin B. Min, Rodney Weber, Nga L. Ng, and Meredith G. Hastings
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Latest update: 17 Dec 2024
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Short summary
We studied how chemicals released from plants and pollution interact in the atmosphere, affecting air quality and climate. By combining laboratory experiments and chemistry models, we tracked unique chemical fingerprints to understand how nitrogen compounds transform to form particles in the air. Our findings help explain the role of these reactions in pollution and provide tools to improve predictions for cleaner air and better climate policies.