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International study finds air pollution leads to millions of hospital visits for asthma attacks worldwide

Air pollution—specifically PM2.5, ozone and NO2—could be to blame for up to 33 million emergency asthma attack visits to hospital a year, according to a new open-access study published in the journal Environmental Health Perspectives.

The researchers aimed to estimate the number of asthma emergency room visits and new onset asthma cases globally attributable to PM2.5, ozone, and NO2 concentrations. They used epidemiological health impact functions combined with data describing population, baseline asthma incidence and prevalence, and pollutant concentrations. They constructed a new dataset of national and regional emergency room visit rates among people with asthma using published survey data.

They 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.

Asthma is the most prevalent chronic respiratory disease worldwide, affecting about 358 million people.

This is the first global study of the potential impacts of air pollution on serious asthma attacks that cause people to visit emergency rooms in hospitals around the world. Previous research by SEI and others have emphasized the impacts of air pollution on the number of premature deaths, but many more people are affected by poor health, through impacts of non-fatal diseases.

—Dr Johan Kuylenstierna, co-author and Policy Director of the Stockholm Environment Institute (SEI)

The international, multi-institutional research team included scientists from the University of York, George Washington University Milken Institute School of Public Health, the University of Colorado Boulder, the Stockholm Environment Institute, the National Aeronautics and Space Administration (NASA), the Japan Agency for Marine-Earth Science and Technology, the Norwegian Meteorological Institute.

Other key findings include:

  • About half of the asthma emergency room visits attributed to dirty air were estimated to occur in South and East Asian countries, notably India and China.

  • Although the air in the United States is relatively clean compared to South and East Asian countries, ozone and particulate matter were estimated to contribute 8 to 21 percent and 3 to 11 percent of asthma ER visits in the United States, respectively.

To estimate the global levels of pollution for this study, the researchers turned to atmospheric models, ground monitors and satellites equipped with remote-sensing devices.

Approximately 95% of the world’s population lives in places with unsafe air. Previously, the Global Burden of Disease Study focused on quantifying the impacts of air pollution on heart disease, chronic respiratory disease, lung cancer, and lower respiratory infections—finding that fine particulate matter and ozone were associated with 4.1 million and 230,000 premature deaths in 2016, respectively.

The research team said that one way to reduce pollutants quickly would be to target emissions from cars, especially in big cities. Such policies would not only help people with asthma and other respiratory diseases, but it would help everyone breathe a little easier.

Support for the study was provided by the NASA Health and Air Quality Applied Science Team, NASA Aura ACMAP, the Stockholm Environment Institute Low Emissions Development Pathways Initiative, and the Global Environment Research Fund of the Japan Ministry of the Environment.


  • Susan C. Anenberg, Daven K. Henze, Veronica Tinney, Patrick L. Kinney, William Raich, Neal Fann, Chris S. Malley, Henry Roman, Lok Lamsal, Bryan Duncan, Randall V. Martin, Aaron van Donkelaar, Michael Brauer, Ruth Doherty, Jan Eiof Jonson, Yanko Davila, Kengo Sudo, and Johan C.I. Kuylenstierna (2018) “Estimates of the Global Burden of Ambient PM2.5, Ozone, and NO2 on Asthma Incidence and Emergency Room Visits” Environmental Health Perspectives doi: 10.1289/EHP3766


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