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Discussion papers
https://doi.org/10.5194/acp-2019-354
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-354
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Apr 2019

Submitted as: research article | 25 Apr 2019

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This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

Ozone formation under low solar radiation in eastern China

Xuexi Tie1,2, Xin Long1, Guohui Li1, Shuyu Zhao1, and Jianming Xu3,4 Xuexi Tie et al.
  • 1KLACP, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China
  • 2Center for Excellence in Urban Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 3Shanghai Meteorological Service, Shanghai, 200030, China
  • 4Shanghai Key Laboratory of Meteorology and Health, Shanghai, 200030, China

Abstract. PM2.5, a particulate matter with a diameter of 2.5 micrometers or less, is one of the major components of the air pollution in eastern China. In the past few years, China's government made strong efforts to reduce the PM2.5 pollutions. However, another important pollutant (ozone) becomes an important problem in eastern China. Ozone (O3) is produced by photochemistry, which requires solar radiation for the formation of O3. Under heavy PM2.5 pollution, the solar radiation is often depressed, and the photochemical production of O3 is prohibited. This study shows that during fall in eastern China, under heavy PM2.5 pollutions, there were often strong O3 photochemical productions, causing a co-occurrence of high PM2.5 and O3 concentrations. This co-occurrence of high PM2.5 and O3 is un-usual and is the main focus of this study. Recent measurements show that there were often high HONO surface concentrations in major Chinese mega cities, especially during daytime, with maximum concentrations ranging from 0.5 to 2 ppbv. It is also interesting to note that the high HONO concentrations were occurred during high aerosol concentration periods, suggesting that there were additional HONO surface sources in eastern China. Under the high daytime HONO concentrations, HONO can be photo-dissociated to be OH radicals, which enhance the photochemical production of O3. In order to study the above scientific issues, a radiative transfer model (TUV; Tropospheric Ultraviolet-Visible) is used in this study, and a chemical steady state model is established to calculate OH radical concentrations. The calculations show that by including the OH production of the photo-dissociated of HONO, the calculated OH concentrations are significantly higher than the values without including this production. For example, by including HONO production, the maximum of OH concentration under the high aerosol condition (AOD = 2.5) is similar to the value under low aerosol condition (AOD = 0.25) in the no-HONO case. This result suggests that even under the high aerosol condition, the chemical oxidizing process for O3 production can occurred, which explain the co-occurrence of high PM2.5 and high O3 in fall season in eastern China. However, the O3 concentrations were not significantly affected by the appearance of HONO in winter. This study shows that the seasonal variation of solar radiation plays important roles for controlling the OH production in winter. When the solar radiation is in a very low level in winter, it reaches the threshold level to prevent the OH chemical production, even by including the HONO production of OH. This study provides some important scientific highlights to better understand the O3 pollutions in eastern China.

Xuexi Tie et al.
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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Interactive discussion
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Xuexi Tie et al.
Xuexi Tie et al.
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Short summary
This study shows that there were often co-occurrences of high PM2.5 and O3 concentrations, which related to high HONO in eastern China. This result suggests that the high daytime HONO can be photo-dissociated to be OH radicals, enhancing chemical production of O3, suggesting that under high aerosol condition, the chemical oxidizing process for O3 production can be occurred in eastern China.
This study shows that there were often co-occurrences of high PM2.5 and O3 concentrations, which...
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