The COVID-19 pandemic and economic shutdown have temporarily produced clearer skies across the U.S. Meanwhile, however, the U.S. Environmental Protection Agency has been busy finding reasons not to pursue long-lasting air quality gains.

On April 30, 2020, the agency published a proposed new rule that retains current National Ambient Air Quality Standards for Particulate Matter without any revisions. It took this action after a five-year review process, in which scientific evidence showed unequivocally that these standards are not adequate to protect public health.

I have studied air pollution and air quality for over 30 years, and have been directly involved for a decade with EPA’s reviews of scientific findings on air pollution. This includes serving on the agency’s Clean Air Scientific Advisory Committee, or CASAC, and on 10 specialized panels focused on individual pollutants.

As I have written previously, the Trump administration has watered down the role of science in what is supposed to be a science-based process of setting national air quality standards. This new proposal – which I expect will be challenged in court when finalized – is the result.

Fine particle air pollution is deadly

Fine particles, known as PM2.5 because they measure 2.5 microns or less in diameter, can penetrate deeply into the lungs and bloodstream. EPA staff scientists have reaffirmed that daily and annual exposure to PM2.5 causes premature death and a variety of illnesses.

Scientists have known this for decades, but since the national standard was last revised in 2012, new studies have strengthened these findings. They include an epidemiologic study with the largest ever number of subjects and several that include PM2.5 concentrations well below the current standard.


EPA’s scientific staff estimates, based on multiple epidemiologic studies, that currently an average of 13,500 to 51,300 people die prematurely each year from breathing fine particles. Although these numbers are uncertain, the likelihood of thousands of deaths per year would typically spur regulators to tighten existing standards. However, EPA’s current political leadership disagrees.

What the law requires

The Clean Air Act directs the EPA to set air quality standards based on an accurate and thorough review of the latest science. This function is performed by CASAC, which I chaired from 2012 to 2015.

CASAC has seven members, which isn’t enough to provide the breadth, depth and diversity of expertise, experience and perspectives needed for these complex reviews. Recognizing this, for four decades the EPA has augmented the committee by convening expert review panels for each pollutant. They include scientists with extensive knowledge of epidemiology, toxicology, medicine, air quality, exposure, risk, statistics and other fields. I served on the 20-member CASAC PM Review Panelthat was appointed in 2015 to help CASAC review the PM2.5 standard.

EPA Administrator Andrew Wheeler disbanded that panel in October 2018. Wheeler also continued a makeover of CASAC, started by his predecessor, Scott Pruitt, that removed leading researchers from the committee. Now CASAC has no epidemiologists – a key discipline for assessing PM2.5 health effects.

What our expert panel recommended

Realizing that EPA would not otherwise get the science advice it needs, the disbanded PM review panel reconvened itself in October 2019. We found that current fine particle standards are not protective of public health.

The studies published since 2012 demonstrating that exposure to fine particles causes premature death at concentrations below current standards were key to our decision. We advised the EPA that the annual standard should be reduced from its current level of 12 micrograms per cubic meter to a range of between 10 and 8 micrograms per cubic meter.


For the 24-hour standard, which regulates short-term air quality spikes, we recommended reducing the limit from the current level of 35 micrograms per cubic meter to between 30 and 25 micrograms per cubic meter. These scientific findings were based on multiple epidemiologic studies, augmented with evidence from controlled experiments with animals and humans.

Failing to protect the public

Administrator Wheeler claims that recent studies since the last time the standards were revised “do not provide a basis for revising the standards.” Wheeler acknowledges that studies based on long-term exposures below the current standards show “associations” between air quality and premature death. However, he argues that this research does not show a causal relationship. Yet, based on the overall body of evidence, he acknowledges that “a causal relationship exists between long-term PM2.5 exposure and total mortality.” In my view, his rationale is illogical and is inconsistent with the evidence.

The Clean Air Act requires regulators to set standards that will provide an “adequate margin of safety.” This means that they should be stringent enough to protect sensitive populations, such as older adults, people with preexisting cardiovascular or respiratory diseases and children with asthma.

The EPA proposal acknowledges that these groups exist, but does not specify how it will protect them from PM2.5 in the air. Wheeler is also silent regarding the role of racial and ethnic differences in exposure and risk, even though a federal court called EPA to task in 2009 for not specifically addressing at-risk groups.

Preliminary evidence suggests that exposure to particles worsens the effects of COVID-19. While this finding needs peer review and additional study, existing evidence of risk for sensitive populations shows the need for a more protective standard.

EPA currently faces lawsuits for multiple instances in which it has either sought to weaken, or failed to strengthen, air pollution regulations. They include rolling back motor vehicle greenhouse gas emission standards, failing to implement stringent rules limiting interstate air pollution and repealing the Obama administration’s Clean Power Plan to limit carbon emissions from power plants. Unless EPA modifies its position on particle air quality to address the law and the science, I expect that this regulation too will end up in court.

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