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Discussion papers
https://doi.org/10.5194/acp-2018-853
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-853
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Sep 2018

Research article | 17 Sep 2018

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

Significant contribution of HONO to secondary pollutants during a severe winter pollution event in southern China

Xiao Fu1, Tao Wang1, Li Zhang1,2, Qinyi Li1,a, Zhe Wang1, Men Xia1, Hui Yun1, Weihao Wang1, Chuan Yu1, Dingli Yue3, Yan Zhou3, Junyun Zheng4, and Rui Han5 Xiao Fu et al.
  • 1Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hong Kong 99907, China
  • 2Atmospheric and Oceanic Sciences, Princeton University, Princeton, New Jersey 08540, USA
  • 3Guangdong Provincial Environmental Monitoring Center, Guangzhou, China
  • 4Institute for Environmental and Climate Research, Jinan University, Guangzhou, China
  • 5National Meteorological Information Center, China Meteorological Administration, Beijing 100081, China
  • anow at: Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Rocasolano, CSIC, Madrid 28006, Spain

Abstract. Nitrous acid (HONO) can strongly affect atmospheric photochemistry in polluted regions through the production of hydroxyl radical (OH). In January 2017, a severe pollution episode occurred in the Pearl River Delta (PRD) of China, with maximum hourly PM2.5, ozone and HONO levels reaching 400µg/m3, 150ppb, and 8ppb, respectively, at a suburban site. The present study investigated the sources/processes generating such high HONO concentrations and the role of HONO chemistry in this severe winter episode. Four recently reported HONO sources were added to the Community Multi-scale Air Quality (CMAQ) model, including RH-dependent and light-enhancing effects on heterogeneous reactions, photolysis of particulate nitrate in the atmosphere, and photolysis of HNO3 and nitrate on surfaces. The revised model reproduced the observed HONO and significantly improved its performance for O3 and PM2.5. The model simulations showed that the heterogeneous generation on surfaces (with RH and light effects) was the largest contributor (72%) to the predicted HONO concentrations, with the RH-enhancing effects more significant at nighttime and the light-enhancing effects more important in the daytime. The photolysis of total nitrate in the atmosphere and deposited on surfaces was the dominant HONO source during noon and afternoon, contributing above 50% of the simulated HONO. The HONO photolysis was the dominant contributor to HOX production in this episode. With all HONO sources, the daytime average O3 at Heshan site was increased by 24ppb (or 70%), compared to the simulation results without any HONO sources. Moreover, the simulated mean concentrations of TNO3 (HNO3 + fine particle NO3) at Heshan site, which was the key species for this haze formation, increased by about 17µg/m3 (67%) due to the HONO chemistry, and the peak enhancement reached 55µg/m3. This study highlights the key role of HONO chemistry in the formation of winter haze in a subtropical environment.

Xiao Fu et al.
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This study has identified the major contributors to the observed high HONO levels during a severe winter pollution episode and highlighted the importance of HONO chemistry in the combined photochemical and haze pollution in a subtropical region.It also highlights the critical need to include/update HONO sources in regional air quality models in order to predict ozone and other secondary pollutants better during heavy pollution events in southern China and similar regions.
This study has identified the major contributors to the observed high HONO levels during a...
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