Short term association between ozone and mortality: global two stage time series study in 406 locations in 20 countries

Objective: To assess short term mortality risks and excess mortality associated with exposure to ozone in several cities worldwide. Design: Two stage time series analysis. Setting: 406 cities in 20 countries, with overlapping periods between 1985 and 2015, collected from the database of Multi-City Multi-Country Collaborative Research Network. Population: Deaths for all causes or for external causes only registered in each city within the study period. MAIN OUTCOME MEASURES: Daily total mortality (all or non-external causes only). Results: A total of 45 165 171 deaths were analysed in the 406 cities. On average, a 10 µg/m3 increase in ozone during the current and previous day was associated with an overall relative risk of mortality of 1.0018 (95% confidence interval 1.0012 to 1.0024). Some heterogeneity was found across countries, with estimates ranging from greater than 1.0020 in the United Kingdom, South Africa, Estonia, and Canada to less than 1.0008 in Mexico and Spain. Short term excess mortality in association with exposure to ozone higher than maximum background levels (70 µg/m3) was 0.26% (95% confidence interval 0.24% to 0.28%), corresponding to 8203 annual excess deaths (95% confidence interval 3525 to 12 840) across the 406 cities studied. The excess remained at 0.20% (0.18% to 0.22%) when restricting to days above the WHO guideline (100 µg/m3), corresponding to 6262 annual excess deaths (1413 to 11 065). Above more lenient thresholds for air quality standards in Europe, America, and China, excess mortality was 0.14%, 0.09%, and 0.05%, respectively. Conclusions: Results suggest that ozone related mortality could be potentially reduced under stricter air quality standards. These findings have relevance for the implementation of efficient clean air interventions and mitigation strategies designed within national and international climate policies. ; WHAT IS ALREADY KNOWN ON THIS TOPIC: Studies on the short term association between ground level ozone and mortality have been mostly performed in a few locations, in limited geographical areas, and using various designs and modelling approaches Although most of the studies found positive associations, results are heterogeneous, and a critical comparison across different countries and regions is made difficult by the limited statistical power and differences across studies Estimates of the association are usually reported as relative risks, a summary measure that does not quantify the actual health impact and makes it difficult to evaluate comparative health benefits of different regulatory limits WHAT THIS STUDY ADDS: This large multi-country study found increased mortality risks associated with exposure to ozone across locations and countries, with an average 0.18% per 10 µg/m3, reinforcing the evidence of a potential causal association Risk estimates were translated in measures of excess mortality, and it was found that more than 6000 deaths each year, corresponding to 0.20% of the total mortality, would have been avoided in the 406 cities studied if countries had implemented stricter air quality standards compliant with the WHO guideline Moreover, smaller but still substantial mortality impacts were found below WHO guideline, supporting the WHO initiative of encouraging countries to revisit current air quality guidelines and enforcing stronger emission restrictions to meet these recommendations ; This work was primarily supported by the UK Medical Research Council (MR/M022625/1 and MR/R013349/1) and by the UK Natural Environment Research Council (NE/R009384/1). HaK was supported by the National Natural Science Foundation of China (91843302 and 91643205) and China Medical Board Collaborating Program (16-250). JM was supported by the Fundação para a Ciência e a Tecnologia (FCT) through the scholarship SFRH/ BPD/115112/2016. VH was supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, PCIN-2017-046) and the German Federal Ministry of Education and Research (BMBF, 01LS1201A2). AU and JK were supported by the Czech Science Foundation (18-22125S). HO and EI were supported by the Estonian Ministry of Education and Research (IUT34-17). AT was supported by the Japanese Society for the Promotion of Science invitational fellowships for research in Japan (S18149). YG was supported by the career development fellowship of the Australian National Health and Medical Research Council (APP1107107 and APP1163693). ST was supported by the Science and Technology Commission of Shanghai Municipality (18411951600). HoK was supported by the Global Research Laboratory (#K21004000001-10A0500-0710) through the National Research Foundation of Korea and by the Future Planning and Korea Ministry of Environment as the “Climate Change Correspondence R&D Program” (2013001310002). RMG was supported by a CSIR parliamentary grant. NS is supported by the National Institute of Environmental Health Sciences funded HERCULES Centre (P30ES019776). The sponsors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of this manuscript. This publication was developed under assistance agreement No RD835871 awarded by the US Environmental Protection Agency to Yale University (MLB). It has not been formally reviewed by EPA. The views expressed in this document are solely those of the authors of the publication and do not necessarily reflect those of the Agency. 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