In spring, ozone (O3) pollution frequently occurrs in eastern China, but key drivers remain uncertain. In this study, interannual variations in springtime ozone in Shanghai, China, from 2013 to 2021, were investigated to assess the health impacts and the effectiveness of recent air pollution control measures. A combination of ground-level measurements of regulated air pollutants, lidar observations, and backward trajectories of air masses was used to identify the key drivers for enhancing springtime O3. The results show that external imports of O3 driven by atmospheric circulation are notable sources of springtime surface O3. For example, the downward transport from the free troposphere could contribute to over 50% of surface O3 in the morning. The surface O3 mixing ratios in spring exhibited an upward trend of 0.93 ppb yr-1 (p < 0.05) from 2013 to 2021. The change in meteorological variables, particularly the increase in air temperature, could explain nearly 87% of the springtime O3 upward trend. The change in anthropogenic emissions of precursors only contributed to a small fraction (<13%) of the increase in springtime O3. The cumulative exposure of urban residents to O3 in spring also exhibited a significant upward trend (111 ppb yr-1, p < 0.05). With the rapid increase in surface O3, premature respiratory mortality attributable to O3 exposure has fluctuated at approximately 2933 deaths per year since 2016, even though the total deaths from respiratory diseases have significantly declined. Long-term exposure to high O3 concentrations is a significant contributor to premature respiratory mortality.
Keywords: Downward transport; Human health effects; Ozone trend; Photochemical pollution; Yangtze river Delta.
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