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Discussion papers
https://doi.org/10.5194/acp-2018-996
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-996
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Nov 2018

Research article | 30 Nov 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

NH3-promoted hydrolysis of NO2 induces explosive growth in HONO

Wanyun Xu1, Ye Kuang2, Chunsheng Zhao3, Jiangchuan Tao2, Gang Zhao3, Yuxuan Bian4, Yingli Yu3, Chuanyang Shen3, Linlin Liang1, and Gen Zhang1 Wanyun Xu et al.
  • 1State Key Laboratory of Severe Weather, Key Laboratory for Atmospheric Chemistry, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, 100081, China
  • 2Institute for Environmental and Climate Research, Jinan University, Guangzhou, China
  • 3Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
  • 4State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, 100081, China

Abstract. The study of atmospheric nitrous acid (HONO), which is the primary source of OH radicals, is crucial to atmospheric photochemistry and heterogeneous chemical processes. The heterogeneous NO2 chemistry under haze conditions was pointed out to be one of the missing sources of HONO on the North China Plain, producing sulfate and nitrate in the process. However, controversy exists between various proposed mechanisms, mainly debating on whether SO2 directly takes part in the HONO production process and what roles NH3 and the pH value play in it. In this paper, never before seen explosive HONO production (maximum rate: 16ppb/hour) was reported and evidence was found for the first time in field measurements during fog episodes (usually with pH>5) and haze episodes under high relative humidity (usually with pH<5), that NH3 was the key factor that promoted the hydrolysis of NO2, leading to explosive growth of HONO and nitrate under both high and lower pH conditions. The results also suggest that SO2 does not directly take part in the HONO formation, but was indirectly oxidized upon the photolysis of HONO through subsequent radical mechanisms. Aerosol hygroscopicity significantly increased with the rapid inorganic secondary aerosol formation further promoting the HONO production. For future photochemical and aerosol pollution abatement, it is crucial to introduce effective NH3 emission control measures, since the NH3-promoted NO2 hydrolysis is a large daytime HONO source, releasing large amounts of OH radicals upon photolysis, which will contribute largely to both atmospheric photochemistry and secondary aerosol formation.

Wanyun Xu et al.
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The study of HONO, the primary source of OH radicals, is crucial to atmospheric photochemistry and heterogeneous chemistry. Heterogeneous NO2 conversion was pointed out to be one of the missing sources of HONO on the North China Plain, but the reaction path is still under debate. In this work, evidence was found that NH3 was the key factor that promoted the hydrolysis of NO2, leading to explosive growth of HONO and nitrate, suggesting that NH3 emission control measures are urgently needed.
The study of HONO, the primary source of OH radicals, is crucial to atmospheric photochemistry...
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