Increases in ozone-related mortality in China over 2013-2030 attributed to historical ozone deterioration and future population aging.

We systematically examine historical and future changes in premature respiratory mortalities attributable to ozone (O) exposure (O-mortality) in China and identify the leading cause of respective change for the first time. The historical assessment for 2013-2019 is based on gridded O concentrations generated by a multi-source-data-fusion algorithm; the future prediction for 2019-2030 uses gridded O concentrations projected by four Coupled Model Intercomparison Project Phase 6 (CMIP6) models under three Shared Socioeconomic Pathways (SSP) scenarios. During 2013-2019, national annual O-mortality is 176.3 thousand (95%CI: 123.5-224.0 thousand) averaged over 2013-2019 with an increasing trend of 14.1 thousand yr (95%CI: 10.2-17.4 thousand yr); sensitivity experiments show that the O-mortality varies at a rate of +12.7 (95%CI: 9.2-15.6), +5.8 (95%CI: 4.0-7.4), +1.0 (95%CI: 0.7-1.2), -5.4 (95%CI: -6.9 to -3.7) thousand yr, owing to changes in O concentration, population age structure, population size, mortality rate for respiratory disease, respectively. The deterioration of O air quality, shown as significant increase in O concentration, is identified as the primary factor which contributes 90.1 % of 2013-2019 O-mortality rise. Compared with O-mortality estimated in this study, the widely-used O-mortality assessment method based on urban-site-dominant O measurements generates close national O-mortality but overestimates (underestimates) provincial O-mortality in coastal (central) provinces. From 2019 to 2030, national O-mortality is projected to increase by 50.4-103.7 thousand under different SSP scenarios. The change in age structure (i.e. population aging) alone will result in significant O-mortality rises of 137.9-160.5 thousand. Compared with 2013-2019 rapid O increase (+2.5 μg m yr at national level), O concentrations are projected to increase at a lower rate (+0.4 μg m yr in SSP5-8.5) or even decrease (-0.7 μg m yr in SSP1-2.6) from 2019 to 2030. Therefore, population aging, in place of O air quality deterioration, will become the leading cause of future O-mortality rises during the coming decade.