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<p>Dinitrogen pentoxide (N<sub>2</sub>O<sub>5</sub>) and nitryl chloride (ClNO<sub>2</sub>) sever as important precursors of nocturnal nitrate, remain poorly measured. In this study, we observed moderate concentrations of N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> in summer Beijing using a chemical ionization mass spectrometer, with ClNO<sub>2</sub> being primarily controlled by the uptake of N<sub>2</sub>O<sub>5</sub> onto particulate chloride. We utilized three methods to quantify nitrate formation through daytime photochemical production (NO<sub>2</sub> + OH·) and nighttime N<sub>2</sub>O<sub>5</sub> heterogeneous hydrolysis. Using chloride as a reference for gas/particle partitioning, we found comparable results with the box model that directly determined the N<sub>2</sub>O<sub>5</sub> uptake coefficient and ClNO<sub>2</sub> yield. The nocturnal nitrate production rates ranged from 0.46 to 2.27 µg m<sup>-3</sup> h<sup>-1</sup>, on average accounting for 31.3% of the total nitrate production. These results indicate the predominance of photochemical processing over heterogeneous hydrolysis in nitrate formation in summer Beijing, different from findings in cold seasons over China that suggest a more important role for N<sub>2</sub>O<sub>5</sub> heterogeneous hydrolysis. Compared to direct measurements of N<sub>2</sub>O<sub>5</sub>-ClNO<sub>2</sub> combined with box model calculations, the chemical transport model slightly overestimated the contributions of N<sub>2</sub>O<sub>5</sub> heterogeneous hydrolysis (34.8%), although it reproduced the increases during periods with high nocturnal nitrate formation. Our study highlights that enhancing the model parametrization, especially considering aerosol composition and seasonal variations, is crucial for more accurate predictions of particulate nitrate levels.</p>

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Role of N2O5 heterogeneous hydrolysis in summer nitrate formation in Beijing: insights from direct measurements and model simulations

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月16日

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  • Wei Zhou,
  • Huiyun Du,
  • Mingyuan Liu,
  • Weiqi Xu,
  • Jian Zhao,
  • Conghui Xie,
  • Qingqing Wang,
  • Zijun Zhang,
  • Zhiqiang Zhang,
  • Jie Li,
  • Weigang Wang,
  • Zifa Wang,
  • Yele Sun

摘要

Dinitrogen pentoxide (N2O5) and nitryl chloride (ClNO2) sever as important precursors of nocturnal nitrate, remain poorly measured. In this study, we observed moderate concentrations of N2O5 and ClNO2 in summer Beijing using a chemical ionization mass spectrometer, with ClNO2 being primarily controlled by the uptake of N2O5 onto particulate chloride. We utilized three methods to quantify nitrate formation through daytime photochemical production (NO2 + OH·) and nighttime N2O5 heterogeneous hydrolysis. Using chloride as a reference for gas/particle partitioning, we found comparable results with the box model that directly determined the N2O5 uptake coefficient and ClNO2 yield. The nocturnal nitrate production rates ranged from 0.46 to 2.27 µg m-3 h-1, on average accounting for 31.3% of the total nitrate production. These results indicate the predominance of photochemical processing over heterogeneous hydrolysis in nitrate formation in summer Beijing, different from findings in cold seasons over China that suggest a more important role for N2O5 heterogeneous hydrolysis. Compared to direct measurements of N2O5-ClNO2 combined with box model calculations, the chemical transport model slightly overestimated the contributions of N2O5 heterogeneous hydrolysis (34.8%), although it reproduced the increases during periods with high nocturnal nitrate formation. Our study highlights that enhancing the model parametrization, especially considering aerosol composition and seasonal variations, is crucial for more accurate predictions of particulate nitrate levels.