Factors driving changes in surface ozone in 44 coastal cities in China

Surface ozone (O3) pollution is an important environmental problem in China. We conducted a comprehensive study to investigate the influence of meteorological factors and emissions on O3 concentrations in 44 coastal cities in China. A Kolmogorov-Zurbenko (KZ) filter was used to decompose the maximum daily average 8-h O3 concentrations (MDA8 O3) into components on different timescales in the coastal cities. It revealed that O3 concentrations in 44 coastal cities increased from 2015 to 2019 and decreased by 4.0% in 2020. The short-term (O3ST), seasonal (O3SN), and long-term components (O3LT) of MDA8 O3 contributed 28.4–71.1% (52.0% on average), 18.4–66.4% (37.9%), and 0.09–14.1% (2.6%) to the total variance, respectively, in the 44 cities during 2015–2020. Overall, the O3 concentrations were more influenced by O3ST in the southern coastal cities, and more influenced by O3SN in the northern coastal cities. Using multiple linear regression, the contributions of meteorology and emissions to O3 concentrations were separated. We estimated that meteorological conditions supported a decrease of 2.1 and 2.9 μg/m3 in O3LT concentration in 2015 and 2016, respectively. While meteorological conditions promoted O3LT concentration increased by 0.3–3.0 μg/m3 during 2017–2020. High nitrogen dioxide (NO2) concentrations, decreasing fine particulate matter (PM2.5) concentrations, and increasing temperature caused an increase in O3 concentrations in several coastal cities. We suggest that controlling NO2 and volatile organic compounds (VOCs) emissions in the future is an effective means of reducing O3 concentrations.