The number of air pollution-related deaths in the United States plunged by almost half in the two decades following passage of the 1990 Clean Air Act Amendments, amounting to about 71,000 by 2010, according to estimates in a newly released study.
Researchers at the University of North Carolina, EPA and other organizations looked at long-term mortality trends stemming from exposure to ground-level ozone and the tiny particulates technically known as PM2.5. From a total of 135,000 in 1990, the number of annual deaths fell 47 percent to end at the 71,000 figure by 2010, the study found. The drop occurred as the nation’s total population swelled by almost one-quarter during that time.
“We’ve invested a lot of resources as a society to clean up our air,” Jason West, a professor of environmental sciences and engineering at UNC Chapel Hill and one of the paper’s authors, said in a news release. “This study demonstrates that those changes have had a real impact.” New federal policies, however, “likely will slow the improvement in air quality,” West added, or possibly make it worse.
The paper, published Friday in the journal Atmospheric Chemistry and Physics, relied on a computer simulation of air pollution across the U.S. The bulk of the decline in deaths from stroke, chronic respiratory disease and other ailments was driven by an almost 40 percent drop in average annual concentrations of PM2.5 during the two decades in question.
Summertime ozone levels fell 9 percent when measured by a one-hour daily maximum. Because other factors also influence overall mortality rates from those diseases, “the drop in deaths was not solely the result of improved air quality,” the release says. The study also notes some uncertainties, such as a possible overestimation of the number of deaths linked to PM2.5 exposure.
Besides the 1990 Clean Air Act Amendments, the paper credits EPA’s Cross-State Air Pollution Rule, which has helped cut power plant releases of ozone-forming nitrogen oxides, along with various policies to reduce car and truck pollution. Even so, both PM2.5 and ozone remain “a great threat to the public health.”
PM2.5 refers to fine particulates that are no more than 2.5 microns in diameter, or roughly one-thirtieth the width of a human hair. Coincidentally, EPA is set to begin collecting public comments tomorrow on a draft assessment citing research that its current standards — last tightened in 2012 — are too weak to adequately protect public health (Greenwire, Oct. 16).
EPA last tightened the national ozone standard in 2015 to 70 parts per billion. Three years later, the U.S. Court of Appeals for the District of Columbia Circuit is set to hear oral arguments in December on a package of litigation that features both industry claims that EPA went overboard in setting the 70 ppb limit and public health groups’ arguments that the evidence warrants cutting the standard to as low as 60 ppb.
While the Trump administration has opted to defend the 70 ppb standard, it has otherwise shown little interest in tightening air pollution regulations and in some cases has sought to roll back Obama-era policies. It’s in the process, for example, of scrapping 2016 control guidelines intended to reduce emissions of volatile organic compounds — another contributor to ozone — from existing oil and gas operations. After proposing the guidelines’ withdrawal earlier this year, EPA plans to issue the final rule by December, according to its latest semiannual regulatory agenda released last week.
The same research team plans to follow up with more work to analyze air pollution since 2010. But the health improvements found so far likely have continued past that date “as air pollutant concentrations have continued to decrease,” Yuqiang Zhang, a Duke University scientist and lead researcher on the study, said in the release.