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BACKGROUND: 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.

OBJECTIVES: We aimed to estimate the number of asthma emergency room visits and new onset asthma cases globally attributable to line particulate matter (PM2.5), ozone, and nitrogen dioxide (NO2) concentrations.

METHODS: We used epidemiological health impact functions combined with data describing population, baseline asthma incidence and prevalence, and pollutant concentrations. We constructed a new dataset of national and regional emergency room visit rates among people with asthma using published survey data.

RESULTS: We estimated that 9-23 million and 5-10 million annual asthma emergency room visits globally in 2015 could be attributable to ozone and PM2.5, respectively, representing 8-20% and 4-9% of the annual number of global visits, respectively. 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, respectively. 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.

CONCLUSIONS: These findings estimate the magnitude of the glohal asthma burden that could he avoided by reducing ambient air pollution. We also identified key uncertainties and data limitations to be addressed to enable relined estimation.