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

Surface ozone (O 3 ) pollution is an important environmental problem in China. We conducted a comprehensive study to investigate the influence of meteorological factors and emissions on O 3 concentrations in 44 coastal cities in China. A Kolmogorov-Zurbenko (KZ) filter was used to decompose the maximum daily average 8-h O 3 concentrations (MDA8 O 3 ) into components on different timescales in the coastal cities. It revealed that O 3 concentrations in 44 coastal cities increased from 2015 to 2019 and decreased by 4.0% in 2020. The short-term (O 3ST ), seasonal (O 3SN ), and long-term components (O 3LT ) of MDA8 O 3 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 O 3 concentrations were more influenced by O 3ST in the southern coastal cities, and more influenced by O 3SN in the northern coastal cities. Using multiple linear regression, the contributions of meteorology and emissions to O 3 concentrations were separated. We estimated that meteorological conditions supported a decrease of 2.1 and 2.9 μg/m 3 in O 3LT concentration in 2015 and 2016, respectively. While meteorological conditions promoted O 3LT concentration increased by 0.3–3.0 μg/m 3 during 2017–2020. High nitrogen dioxide (NO 2 ) concentrations, decreasing fine particulate matter (PM 2.5 ) concentrations, and increasing temperature caused an increase in O 3 concentrations in several coastal cities. We suggest that controlling NO 2 and volatile organic compounds (VOCs) emissions in the future is an effective means of reducing O 3 concentrations.