Canadian Study: Most Population Centers Exceed WHO PM2.5 Standards

A study published March 16 ahead of print in the peer-reviewed journal Environmental Health Perspectives (EHP) finds that many developing countries have high long-term levels of aerosol air pollution.

The study is the first to use satellite data to estimate long-term fine particulate matter (PM2.5) concentrations across the entire globe.

PM2.5 consists of particles with a diameter of 2.5 micrometers (the size of many bacteria) or smaller and comes from such sources as forest fires, power plants, cars, industry, and in many countries, home heating and cooking. These particles pose a health concern because of their ability to penetrate deep into the lungs once they are breathed in.

The study found that 80 percent of the global population lives in places where concentrations of PM2.5 exceed the ultimate air quality guideline set by the World Health Organization (WHO) of 10 micrograms per cubic meter (µg/m3). The WHO has set several interim targets, the highest of which is 35 µg/m3, and even that is exceeded over central and eastern Asia for 38 percent and 50 percent of the population, respectively. Eastern China showed high levels of pollution; large regions showed an annual average of more than 80 µg/m3.

The study used satellite data gathered over a span of six years, providing some of the first long-term measurements of average PM air pollution concentrations for many regions with significant sources of air pollution but few if any ground-level sampling stations to substantiate the extent of human exposures — including many developing countries.

The methods described and validated by the study can be applied to further studies of health effects caused by exposure to PM air pollution around the world. These methods include combining data from different satellite instruments with a chemical-transport model to relate observations of the entire air column beneath the satellite to air quality near the surface. The authors validated this approach by comparing their estimates to those derived from ground-based sampling and found a significant level of agreement. However, they note additional research is needed to reduce uncertainty due to non-uniform satellite sampling, cloud cover, and other factors that may limit the accuracy of the satellite-based estimates.

The study is the first to combine data from two particular satellite instruments—MODIS (Moderate Resolution Imaging Spectroradiometer) and MISR (Multi-angle Imaging SpectroRadiometer)—on a global scale.

Authors of the article are Aaron van Donkelaar, Randall V. Martin, Michael Brauer, Ralph Kahn, Robert Levy, Carolyn Verduzco, and Paul J. Villeneuve. This work was supported by Health Canada and by graduate fellowships from the Natural Science and Engineering Research Council of Canada and the Killam Trust.

EHP is published by the National Institute of Environmental Health Sciences, part of the U.S. Department of Health and Human Services. EHP is an open access journal.

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