Abstract
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 h 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 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 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 many parts of China. The long-range transport of ozone and its precursors from outside the modeling domain also contributed to the increase in MDA8 O3 in China, especially on the Qinghai–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.
Highlights
Elevated concentrations of ozone (O3) on the earth’s surface are harmful to human health and terrestrial vegetation (Lefohn et al, 2018; Lelieveld et al, 2015; Fleming et al, 2018)
Cheng et al (2019) applied the Kolmogorov–Zurbenko filtering method to the ozone variations in Beijing from 2006 to 2017, and the results suggested that the relative contribution of meteorological conditions to long-term variation in ozone was only 2 % to 3 %, but short-term ozone concentrations were affected significantly by variations in meteorological conditions
We further found that in some specific regions and years, the changes in maximum daily 8 h average (MDA8) O3 due to meteorological variation could be comparable to or greater than those due to emission changes, which highlights the significant role of meteorological conditions in ozone variations
Summary
Elevated concentrations of ozone (O3) on the earth’s surface are harmful to human health and terrestrial vegetation (Lefohn et al, 2018; Lelieveld et al, 2015; Fleming et al, 2018). With rapid urbanization and economic development, the ozone concentrations in the troposphere have increased in the past decades over most regions of Asia, including China Wang et al, 2019; Xu et al, 2016; Ziemke et al, 2019), and ground-level ozone pollution has become a major concern in China’s urban and industrial regions (Wang et al, 2017; Verstraeten et al, 2015). The Chinese Ministry of Ecology and Environment reported that the observed concentrations of primary pollutants had decreased significantly since these strict control measures (http://www.mee.gov.cn, last access: 1 December 2019).
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