Daily exposure to ground level ozone is associated with increased mortality, suggest the findings of an analysis of data from over 400 cities in 20 countries.
The study, published in the BMJ, suggests more than 6,000 deaths could be avoided annually in the selected cities if stricter air quality standards were implemented.
The study used data from the Multi-City Multi-Country Collaborative Research Network to derive daily average ozone levels, particulate matter, temperature, and relative humidity at each location to estimate the daily number of extra deaths attributable to ozone.
A total of 45,165,171 deaths were analysed in 406 cities. On average, a 10 µg/m3 increase in ozone during the current and previous day was associated with a 0.18 per cent increased risk of death. This equates to 6,262 extra deaths each year (0.2% of total mortality) in the 406 cities that could potentially have been avoided if countries had implemented stricter air quality standards in line with the World Health Organization guideline, the authors said.
This observational study had some limitations. Areas such as South America, Africa, and the Middle East were not represented or not assessed, and differences in monitoring and data collection between countries may have affected the accuracy of the estimates.