Long-term trend of ozone pollution in China during 2014–2020: distinct seasonal and spatial characteristics and ozone sensitivity

Abstract

Abstract. In the past decade, ozone (O3) pollution has become a severe environmental problem in China's major cities. Here, based on available observational records, we investigated the long-term trend of O3 pollution in China during 2014–2020. The O3 concentrations were slightly higher in urban areas than in non-urban areas. During these 7 years, the highest O3 concentrations primarily occurred during summer in northern China, and during autumn or spring in southern China. Although O3 precursors, including nitrogen oxides (NOx) and carbon monoxide (CO), continuously decreased, O3 concentrations generally increased throughout the 7 years with a slower increasing rate after 2017. The long-term trend of O3 concentrations differed across seasons, especially from 2019 to 2020, when O3 concentrations decreased in summer and increased in winter. To analyse the causes of this observed trend, a photochemical box model was used to investigate the change in the O3 sensitivity regime in two representative cities – Beijing and Shanghai. Our model simulations suggest that the summertime O3 sensitivity regime in urban areas of China has changed from a VOC-limited regime to a transition regime during 2014–2020. By 2020, the urban photochemistry was in a transition regime in summer but in a VOC-limited regime in winter. This study helps to understand the distinct trends of O3 in China and provides insights into efficient future O3 control strategies in different regions and seasons.

Diagnosing ozone–NOx–VOC sensitivity and revealing causes of ozone increases in China based on 2013–2021 satellite retrievals

“…Currently, the VOC-limited regime exists in most major urban clusters in China, which are also areas with high ozone levels. The exploration of the causes of ozone rise in China illustrates the current need for VOC control, which is consistent with the findings of previous studies on major cities and city clusters (Wang et al, 2022;Yang et al, 2019). Appropriate reduction ratios of VOC and NO x emission can control both PM 2.5 and O 3 pollution, which is suggested by the simultaneous decline in O 3 and PM 2.5 concentrations in Beijing in recent years (Ren et al, 2021).…”

Distinct Seasonality in Aerosol Responses to Emission Control Over Northern China

“…In fact, some observational studies have illustrated the hygroscopic capacity of the aged secondary OA (Hong et al., 2018; Kuang et al., 2020; Xu et al., 2020). Unlike the strong reduction of primary aerosols, there is evidence suggesting the enhancement of secondary aerosol formation in winter due to the rising atmospheric oxidizing capacity (Wang, Gao, et al., 2022; Wang, Parrish, et al., 2022). If this is the case for secondary OA, a consideration of its hygroscopicity would imply an additional offset on the AOD decline effect from PM 2.5 reduction in winter.…”

Large Modeling Uncertainty in Projecting Decadal Surface Ozone Changes Over City Clusters of China

“…Earlier worsening ozone pollution, from 2013 to 2017, have been attributed to ozone's nonlinear response to large reductions in nitrogen oxides (NO x ) emissions without equivalent reductions in volatile organic compounds (VOCs) emissions (Y. Liu & Wang, 2020b; N. Wang et al., 2019; T. Wang et al., 2017), particularly in many urban regions that were within the NO x ‐saturated regime (H. Lu et al., 2019; Ou et al., 2016). Nevertheless, with the continuous reductions in NO x , the sensitivity of summertime ozone production to VOCs in some urban areas of China may have gradually weakened (W. Wang et al., 2021, 2022). Furthermore, it has been suggested that the turning point between NO x ‐saturated and NO x ‐limited regimes in some densely populated urban areas of China was reached in 2019 (Chen et al., 2021).…”