LAUSR

Abstract Background Previous studies have shown that exposure to ozone is associated with mortality. Reducing indoor ozone of outdoor origin may be an effective short-term method to reduce overall ozone exposure and the associated premature mortality. Here, we estimated (1) premature mortalities attributable to ozone for individuals aged 25 years and over in urban China, (2) the proportion of this mortality associated with time indoors, and (3) the mortality that might be achieved by meeting the current Chinese Indoor Air Quality Standard (IAQS) or Assessment Standard for Healthy Buildings (ASHB), as well as more stringent guidelines. Methods Outdoor ozone concentrations were measured hourly at all 1497 government monitoring stations (as at 2015) located in 339 cities dispersed across China, and these data were used to estimate premature mortality in 2015 from circulatory and respiratory causes based on a concentration–response model derived from an extended analysis of the American Cancer Society Cancer Prevention Study II. We used estimated air exchange rates, ozone penetration factors, and ozone surface removal rates to estimate the corresponding indoor ozone concentrations for the hourly outdoor ozone measurements. Finally, we estimated mortality reductions that might be achieved in urban China by meeting different 1-h indoor ozone standards or guidelines. Findings We estimated that there were 61 000 premature deaths from respiratory and cardiovascular disease attributable to ozone among individuals aged 25 years or over in urban China in 2015. Indoor exposures accounted for 87% (53 000) of this total. If the current indoor ozone standards (IAQS 80 ppb; ASHB 56 ppb) were met, the reduction in total mortality would be indistinguishable from zero. To be meaningful, an indoor standard should be no higher than 30 ppb. Interpretation Regardless of whether a person is outdoors or indoors, the mortality risks associated with long-term ozone exposure are derived using data from outdoor ozone monitoring stations. Outdoor concentrations of ozone are substantially higher than the time-matched estimates of indoor ozone concentrations, reflecting the reactive chemistry of ozone indoors. Globally, guidelines for indoor ozone concentrations should be substantially lower than guidelines for outdoor ozone concentrations to account for both ozone and its indoor reaction products. Funding Natural Science Foundation of China (numbers 51420105010 and 51521005) and the National Key Research and Development Program of China (number 2017YFC0702700).