Asthma is the most prevalent chronic respiratory disease worldwide, affecting 358 million people in 2015. Ambient air pollution exacerbates asthma among populations around the world and may also contribute to new-onset asthma.

The study estimates the number of asthma emergency room visits and new onset asthma cases globally attributable to fine particulate matter (PM2.5), ozone, and nitrogen dioxide (NO2) concentrations.

Methods included epidemiological health impact functions combined with data describing population, baseline asthma incidence and prevalence, and pollutant concentrations, as well as a new dataset of national and regional emergency room visit rates among asthmatics using published survey data.

The authors estimate that 9-23 and 5-10 million annual asthma emergency room visits globally in 2015 could be attributable to ozone and PM2.5, representing 8-20% and 4-9% of the annual number of global visits. The range reflects the application of central risk estimates from different epidemiological meta-analyses. Anthropogenic emissions were responsible for ~37% and 73% of ozone and PM2.5 impacts. Remaining impacts were attributable to naturally-occurring ozone precursor emissions (e.g. from vegetation, lightning) and PM2.5 (e.g. dust, sea salt), though several of these sources are also influenced by humans. The largest impacts were estimated in China and India.

The findings estimate the magnitude of the global asthma burden that could be avoided by reducing ambient air pollution. The study also identifies key uncertainties and data limitations to be addressed to enable refined estimation.