The Clean Air Act of 1970 set nationwide air quality standards and motor-vehicle emissions standards for the first time, and the federal government and some states have continued to take steps to tackle air pollution.
Thanks to these efforts, U.S. air quality has improved. Pope and his team decided to use U.S. data on fine-particulate matter concentrations and life expectancy from the late 1970s and the late 1990s as a “natural experiment” to determine whether cleaner air had any effect on health.
They plotted pollution data for 1979–1983 to 1978–1982 life expectancies for 217 counties within 51 metropolitan areas around the country. Then they compared 1999–2000 pollution data to 1997–2001 life expectancies. Finally, they looked at how changes in life expectancy related to changes in air pollution for both time periods.
Many other factors can boost life expectancy, such as increases in income and education and reductions in smoking prevalence, so the researchers used statistical techniques to control for these and other relevant factors. After this adjustment, they found that the effect of air pollution reduction remained; for every 10 microgram per cubic meter decrease in fine-particulate air pollution, life expectancies rose by about seven months. Pollution levels averaged about 21 micrograms per cubic meter in 1979–1983 and had fallen to an average of 14 micrograms per cubic meter by 1999–2000.
Life expectancy for the corresponding time periods rose from age 74 to 77. Pope and his team calculate that reductions in air pollution accounted for as much as 15% of the increase in life expectancy.
While there is plenty of research linking air pollution to increased mortality and worse health, noted Daniel Krewski, PhD, a professor of epidemiology and medicine at the University of Ottawa, the current study is among the first to show how cleaning up pollution affects health. “It’s a very important contribution,” said Krewski, who wrote an editorial accompanying the study.
Bert Brunekreef, PhD, director of the Institute for Risk Assessment Sciences at the University of Utrecht in the Netherlands, said the current study could help encourage government and industry to address air pollution in parts of the world where it is a serious threat to health. “Showing public health benefits of changes in pollution is a strong message, comparable to studies documenting health benefits of smoking bans,” he said via email.
According to the Environmental Protection Agency, particulate matter 2.5 microns in size declined in the United States by an average of 11% between 2000 and 2007.
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