Preprints
https://doi.org/10.5194/egusphere-2025-2765
https://doi.org/10.5194/egusphere-2025-2765
24 Jul 2025
 | 24 Jul 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Measurement report: Anthropogenic activities reduction suppresses HONO formation: Direct evidence for Secondary Pollution control

Mingzhu Zhai, Shengrui Tong, Wenqian Zhang, Hailiang Zhang, Xin Li, Xiaoqi Wang, and Maofa Ge

Abstract. Nitrous acid (HONO) is a key precursor of atmospheric hydroxyl radicals (OH) and significantly influences the formation of secondary pollutants, making it essential for understanding and controlling air pollution. While many studies have focused on its formation mechanisms, few have explored the impact of anthropogenic activities variation on HONO formation. Therefore, we investigated the impact of anthropogenic activities variation on HONO formation based on a comprehensive observation conducted in urban Beijing during autumn and winter of 2022. During clean periods with a 53 % drop in Traffic Performance Index, HONO, CO, and NO2 levels decreased by 2–3 times compared to polluted periods and significantly lower than previously reported wintertime levels in Beijing. Source apportionment revealed that NO2 heterogeneous reaction on ground was the dominant HONO source across all periods. Vehicle emissions contributed more to HONO during clean periods, suggesting that reduced anthropogenic activities has a stronger influence on secondary HONO formation. NO3- photolysis contributed more to HONO during polluted periods, due to higher NO3- fractions in PM2.5 under more polluted conditions. Despite including all known formation pathways in the model, unidentified HONO sources still remain. This is strongly associated with intense solar radiation and high OH concentrations at daytime, as well as elevated NH3 concentrations at nighttime. Emission reduction simulations further revealed that a 50 % NOx reduction during polluted periods could lower HONO by up to 38.4 %, directly demonstrating that reducing anthropogenic activities significantly suppresses HONO formation and provides a scientific basis for the development of air pollution control strategies.

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Mingzhu Zhai, Shengrui Tong, Wenqian Zhang, Hailiang Zhang, Xin Li, Xiaoqi Wang, and Maofa Ge

Status: open (until 04 Sep 2025)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-2765', Dianming Wu, 06 Aug 2025 reply
  • RC2: 'Comment on egusphere-2025-2765', Anonymous Referee #2, 01 Sep 2025 reply
Mingzhu Zhai, Shengrui Tong, Wenqian Zhang, Hailiang Zhang, Xin Li, Xiaoqi Wang, and Maofa Ge

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Measurement report: Anthropogenic activities reduction suppresses HONO formation: Direct evidence for Secondary Pollution control Mingzhu Zhai et al. https://doi.org/10.5281/zenodo.16083849

Mingzhu Zhai, Shengrui Tong, Wenqian Zhang, Hailiang Zhang, Xin Li, Xiaoqi Wang, and Maofa Ge

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Short summary
To explore how anthropogenic activities affect HONO formation, we conducted comprehensive observations in Beijing. During clean periods with a 53 % drop in Traffic Performance Index, HONO, CO, and NO2 levels decreased by 2–3 times compared to polluted periods. Emission reduction simulations showed that a 50 % NOx reduction could lower HONO by up to 38.4 %, indicating that reducing anthropogenic activities significantly suppresses HONO formation and provides direct evidence for pollution control.
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