Smog isn't just annoying, it's also deadly: Exposure to even small amounts of toxic air pollutants is linked to increased cardiovascular and respiratory death rates, according to a new international study.
The study, published Wednesday in the New England Journal of Medicine, is the largest ever undertaken to investigate the short-term impacts of air pollution on death. It was conducted over 30 years in 652 cities in 24 countries.
The study looked at tiny particles of pollution known as particulate matter (PM).
"The smaller the airborne particles, the more easily they can penetrate deep into the lungs and absorb more toxic components, causing death,” said study lead author Yuming Guo from Monash University's School of Public Health in Melbourne, Australia.
Guo said there is no threshold for the association between particulate matter and mortality: "Even low levels of air pollution can increase the risk of death," he said.
Particulate matter is a mixture of solid particles and liquid droplets found in the air, according to the Environmental Protection Agency. Some particles, such as dust, dirt, soot or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope.
The two main categories of particulate matter are PM2.5 and PM10; the number represents the diameter of each particle in microns.
In the U.S., Guo said "the effects of both PM2.5 and PM10 on death are higher than the global average. This means people in the U.S. are more sensitive to daily increase of air pollution than many other countries."
Many studies have examined particulate matter and mortality, but most of those were based on single cities, regions or countries, U.S. News and World Report said. This study's method and scope were broader, however, allowing researchers to examine and compare particulate matter concentrations with deaths from all causes at the global, regional and national levels.
Chris Griffiths, a professor of primary care at Queen Mary University of London, told Science Media Centre that the study shows that in cities across six continents, the higher the pollution levels, the faster people are dying.
"These are avoidable deaths," he said. "Most concerning is that deaths relating to pollution occur at levels below international recommended pollution limits. The authors provide the strongest evidence yet that target air pollution levels are set too high."
This article originally appeared on USA TODAY: Air pollution linked to early deaths, study says