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

Abstract

OBJECTIVE To assess short term mortality risks and excess mortality associated with exposure to ozone in several cities worldwide. DESIGNTwo 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. POPULATIONDeaths for all causes or for external causes only registered in each city within the study period. MAIN OUTCOME MEASURESDaily total mortality (all or non-external causes only). RESULTSA total of 45 165 171 deaths were analysed in the 406 cities. On average, a 10 µg/m 3 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/ m 3 ) 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/m 3 ), 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. CONCLUSIONSResults 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.Cite this as: BMJ 2020;368:m108 http://dx. WHAT IS ALREADY KNOWN ON THIS TOPICStudies 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 ADDSThis 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...

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