Not all air pollution is of the kind that casts a pall over major metropolises like Los Angeles or Shanghai. One form consists of particles so tiny (1/30 the diameter of a human hair) that it is not only invisible but also capable of evading the body’s defenses and lodging deep in the lungs — where it can be deadly.
Researchers have had no reliable global picture of the full, long-term scope of the problem — until the map above was published earlier this summer in the journal Environmental Health Perspectives, and yesterday online by NASA. In the map, high concentrations of fine particulate pollution is shown in yellows, oranges and reds.
Fine particulate matter, or PM2.5 (because individual particles are less than 2.5 micrometers in diameter), consists of dust, soot and smoke. According to a report in the journal Science:
Hundreds of studies have suggested that breathing fine particles spewed by vehicles, factories, and power plants can trigger heart attacks and worsen respiratory disease in vulnerable people, leading to perhaps 60,000 premature deaths a year in the United States.
And worldwide, the death toll is believed to be in the millions.
The United States and several European countries monitor these fine particulates at numerous sites. Even so, the geographic coverage of the monitoring is limited, according to the study in Environmental Health Perspectives. And few long-term monitoring sites exist elsewhere in the world, “particularly in rapidly developing countries where concentrations and estimated health impacts are greatest.”
Aaron van Donkelaar of Dalhousie University, in Halifax, Nova Scotia and a group of colleagues used measurements from two instruments on NASA satellites, along with computer modeling, in an attempt to overcome previous limitations in space-based measurements of fine particulates. Based on their results, they estimate that 80 percent of the world’s population breathe polluted air that exceeds the World Health Organization’s Air Quality Guideline, or AGQ, of less than 10 micrograms per cubic meter (10 µg/m3).
As the map reveals, fine particulate pollution is particularly high in several regions in China. In eastern China, concentrations reach 60 to 90 µg/m3, with values greater than 100 µg/m3 in major industrial regions. In India, from New Delhi eastward, values of 80 to 100 µg/m3 are common, especially in winter.
The World Health Organization has acknowledged that reducing fine particulate pollution below the 10 microgram per cubic meter level would “appear impossible in situations where air pollution levels greatly exceed the recommended guideline levels.” So it has recommended a gradual approach to improving air quality. They’ve recommended a set of interim targets “to promote a shift from high air pollutant concentrations, which have acute and serious health consequences, to lower air pollutant concentrations.”
But Donkelaar and his colleagues found that large swaths of Asia exceed even these interim targets:
. . . half (50%) of the eastern Asian population lives in regions that exceed the WHO Air Quality Interim Target-3 of 35 µg/m3 and are therefore at increased risk from air pollution-related health impacts. These results highlight the potential use of satellite aerosol observations to contribute to studies on the chronic effects of air pollution at regional and global scales.
In the United States, the highest concentrations of fine particulates are located in urban areas of the Midwest and East: