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Air pollution concentrations within or below current air quality standards have contributed to thousands of deaths in the U.S. from cardiorespiratory causes, researchers reported.

In the nationwide and county level analysis accessing the impact of particulate matter pollution (PM_2.5) concentrations on mortality and health, as many as 30,000 deaths in the U.S. could be attributed to breathing air with PM_2.5 levels from 2.8 µg/m³ to 13.2 µg/m³ from 1999 through 2015, estimated Majid Ezzati, PhD, of Imperial College London, and colleagues in .

This level of air pollution has generally been considered safe by regulatory agencies, but in 2012, the updated the National Ambient Air Quality Standard for fine particulate pollution, reducing the annual standard from 15 µg/m³ to 12 µg/m³.

Ezzati's group analyzed PM_2.5 concentrations across all counties in the contiguous U.S. (excluding Alaska and Hawaii) recorded at 750 air quality monitoring stations during the decade and a half from 1999 to 2015.

They then compared this with data from the National Center for Health Statistics vital registration, which recorded a total of 41.9 million deaths during the period, with 18.4 million deaths attributed to cardiorespiratory disease.

Publicly available data on characteristics within counties that could influence mortality were also included in the analysis. The characteristics included per capita income, racial makeup, education level, unemployment, urban dwelling, and smoking history.

The highest PM_2.5 concentration during the study period were recorded in California's Tulare County in 1999 (13.2 µg/m³), and the lowest levels were recorded in Apache County, Arizona (2.8 µg/m³).

PM_2.5 concentrations were below the current national ambient air quality standards for particle pollution of 12 µg/m³ in every county except four.

National, population-weighted average PM_2.5 concentrations declined from 13.6 µg/m³ in 1999 to 8.0 µg/m³ in 2015.

"Pollution reduction was largest in the most polluted areas, such as southern California and some southern states (Alabama and Georgia) where PM_2.5 declined by more than 10 µg/m³ from 1999 to 2015," the researchers wrote.

They used four Bayesian spatiotemporal models adjusted for other causes of death "to directly estimate mortality and life expectancy loss due to current PM_2.5 pollution and the benefits of reductions since 1999, nationally and by county."

Combined data analysis suggested an increase in deaths due to air pollution exposures at PM_2.5 levels of 1 µg/m³ and higher.

They estimated that from 1999 through 2015, 15,612 women and 14,757 men in the U.S. died from cardiorespiratory causes related to PM_2.5 exposures.

The researchers calculated that the deaths lowered national life expectancy by an estimated 0.15 years among women (95% credible interval 0.13-0.17) and 0.13 years for men (95% credible interval 0.11-0.15).

"At any PM_2.5 concentration, life expectancy loss was, on average, larger in counties with lower income and higher poverty rates than in wealthier counties," they wrote.

"We've known for some time that these particles can be deadly," Ezzati noted in a written press statement. "This study suggests even at seemingly low concentrations -- mostly below current limits -- they still cause tens of thousands of deaths. Lowering the PM_2.5 standard below the current level is likely to improve the health of the U.S. nation and reduce health inequality."

The researchers warned that the current in the U.S. federal government could result in poorer air quality and higher mortality, and specifically identified recent EPA moves "that constrain the evaluation of health effects of air pollution to publicly available datasets."

In April 2018 at an event closed to the press, then EPA Administrator Scott Pruitt requiring that studies used to develop EPA regulations be limited to those with data available for public scrutiny.

The move was promoted by Pruitt as a way to increase transparency, but experts warned that it would exclude key studies used to evaluate the impact of air pollution on human health.

The rule change was immediately opposed by health groups, including the American Thoracic Society (ATS).

At a press conference at the 2018 ATS annual meeting in San Diego, executive director Stephen C. Crane, PhD, charged that the policy change was one more effort by the agency's current leadership "to marginalize the input of science and scientists into EPA's decision making."

"This seemingly innocuous policy proposal may have a more insidious side that will alternately reduce the ability of science and scientists to help shape EPA policy," he said.

In June 2019, acting EPA Administrator Andrew Wheeler related to the agency. The policy grants the EPA administrator authority to decide which public records would be released by EPA under the Freedom of Information Act.

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