More than 9 in 10 people breathe bad air, WHO study says

HONG KONG — The World Health Organization said Tuesday that 92 percent of people breathe what it classifies as unhealthy air, in another sign that atmospheric pollution is a significant threat to global public health.

A new report, the WHO’s most comprehensive analysis so far of outdoor air quality worldwide, also said about three million deaths a year — mostly from cardiovascular, pulmonary and other noncommunicable diseases — were linked to outdoor air pollution. Nearly two-thirds of those deaths are in Southeast Asia and the Western Pacific region, compared with 333,000 in Europe and the Americas, the report said.

“When you look out through the windows in your house or apartment, you don’t see the tiny little particles that are suspended in the air, so the usual perception is that the air is clean,” Rajasekhar Balasubramanian, an air quality expert at the National University of Singapore who was not involved in the study, said in a telephone interview on Tuesday.

“But the WHO report is a clear indication that even in the absence of air pollution episodes, the concentrations of particles suspended in the air do exceed what’s considered to be acceptable from a health viewpoint,” he said.

In previous studies, the WHO estimated that more than 8 in 10 people in urban areas that monitored air pollution were breathing unhealthy air and that about 7 million deaths a year were linked to indoor and outdoor pollution. The new study reduced the second estimate to 6.5 million deaths. But Maria Neira, director of the WHO’s Department of Public Health and Environment, said in a telephone interview that “the trends are still going in the wrong direction.”

“Somebody has to pay for those health systems to sustain the treatment and the care for those chronic patients, and this is something that countries need to balance when they make decisions about the sources of energy they are selecting or the choices they make in terms of public transport,” Dr. Neira said.

The WHO study was conducted by dozens of scientists over 18 months and was based on data collected from satellites, air-transport models and ground monitors in more than 3,000 urban and rural locations, agency officials said Tuesday. The agency defined unhealthy air as having concentrations of fine particulate matter, known as PM 2.5, above 10 micrograms per cubic meter, or 35.3 cubic feet, but it did not measure concentrations of ozone, nitrous oxide or other harmful pollutants.

The study said that major drivers of global air pollution included inefficient energy use and transportation.

“People think of air pollution as a respiratory disease,” said Carlos Dora, who heads the WHO’s air pollution team. “And in fact, it’s heart disease, strokes and cardiovascular. Because there’s very small particles that go into the blood … the damage air pollution does to the vessels is similar to the damage that cholesterol or high blood pressure do. That has changed a lot the picture.”