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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 09 Jan 2020

Submitted as: research article | 09 Jan 2020

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

Worsening urban ozone pollution in China from 2013 to 2017 – Part 1: The complex and varying roles of meteorology

Yiming Liu and Tao Wang Yiming Liu and Tao Wang
  • Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, 999077, China

Abstract. China has suffered from increasing levels of ozone pollution in urban areas despite the implementation of various stringent emission reduction measures since 2013. In this study, we conducted numerical experiments with an up-to-date regional chemical transport model to assess the contribution of the changes in meteorological conditions and anthropogenic emissions to the summer ozone level from 2013 to 2017 in various regions of China. The model can faithfully reproduce the observed meteorological parameters and air pollutant concentrations and capture the increasing trend in the surface maximum daily 8-hour average (MDA8) ozone (O3) from 2013 to 2017. The emission control measures implemented by the government induced a decrease in MDA8 O3 levels in rural areas but an increase in urban areas. The meteorological influence on the ozone trend varied by region and by year and could be comparable to or even more significant than the impact of changes in anthropogenic emissions. Meteorological conditions can modulate the ozone concentration via direct (e.g., increasing reaction rates at higher temperatures) and indirect (e.g., increasing biogenic emissions at higher temperatures) effects. As an essential source of volatile organic compounds that contributes to ozone formation, the variation in biogenic emissions during summer varied across regions and was mainly affected by temperature. China’s midlatitude areas (25° N to 40° N) experienced a significant decrease in MDA8 O3 due to a decline in biogenic emissions, especially for the Yangtze River Delta and Sichuan Basin regions in 2014 and 2015. In contrast, in northern (north of 40° N) and southern (south of 25° N) China, higher temperatures after 2013 led to an increase in MDA8 O3 concentrations via an increase in biogenic emissions. We also assessed the individual effects of changes in temperature, specific humidity, wind field, planetary boundary layer height, clouds, and precipitation on ozone levels from 2013 to 2017. The results show that the wind field change made a significant contribution to the increase in surface ozone over China by transporting the ozone downward from the upper troposphere and the lower stratosphere. The long-range transport of ozone and its precursors outside the modeling domain also contributed to the increase in MDA8 O3 in China, especially on the Tibetan Plateau (an increase of 1 to 4 ppbv). Our study represents the most comprehensive and up-to-date analysis of the impact of changes in meteorology on ozone across China and highlights the importance of considering meteorological variations when assessing the effectiveness of emission control on changes in the ozone levels in recent years.

Yiming Liu and Tao Wang
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Status: open (until 05 Mar 2020)
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Yiming Liu and Tao Wang
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Short summary
This study revealed the effects of changes in meteorology and anthropogenic emissions on the summer ozone variations from 2013 to 2017 across China by conducting numerical experiments. We highlighted the important but varying roles of meteorology in ozone variations attributed to the synergistic or counteracting effects from individual meteorological factors. Developing future ozone pollution mitigation policies should consider the counteracting impact of meteorological changes.
This study revealed the effects of changes in meteorology and anthropogenic emissions on the...