Poor air quality has been linked to Covid-19 impacts. Trump's EPA is still limiting pollution restrictions.

But for all the mysteries that scientists are still working to solve, we have known from the start that this virus unleashes a brutal assault on the respiratory system, and is especially dangerous for people with lung and heart disease.

Scientists have known for decades that air pollution also attacks the lungs and cardiovascular system -- contributing to 4.2 million premature deaths annually globally and increasing risks for a host of other conditions, many of which put people at greater risk of serious illness from the coronavirus.

A new Harvard study has further connected the dots, showing a link between exposure to air particle pollution and severe cases of coronavirus.

Despite the evidence, the Trump administration has continued its quest to limit restrictions on the fossil fuel industry, which is the source of much of this pollution.

The Environmental Protection Agency has said its moves protect public health and are reasonable regulatory decisions that respect the law.

But some scientists and legal experts say the moves reflect a dangerous disregard for science in the middle of a deadly pandemic, and could be used to further weaken protections down the road.

EPA elects to leave air pollution standards untouched

Air pollution has long been a public health hazard, but in mid-April after a lengthy review, the EPA proposed leaving the existing standards for two kinds of fine-particle air pollution unchanged.

The main type of pollution in question -- PM 2.5 -- are microscopic particles that float in the air we breathe and measure barely a fraction of the diameter of a human hair.

They're sent into the air by power plants, cars and other sources that burn fossil fuels, as well as by wildfires. And despite their small size, the particles have been linked to serious cardiovascular and respiratory problems.

The current PM 2.5 standard requires air particle levels to be limited to 12 micrograms per cubic meter.

But the EPA's draft review in September 2019 estimated that the current PM 2.5 standards are associated with 45,000 deaths annually, and tightening them to 9 micrograms per cubic meter could reduce deaths by up to 27%.

Still, the EPA decided to leave the regulations untouched.

"Based on review of the scientific literature and recommendation from our independent science advisors, we are proposing to retain existing PM standards which will ensure the continued protection of both public health and the environment," EPA Administrator Andrew Wheeler said in an April 14 statement justifying the move.

The connection between Covid-19 and air pollution

Scientists and environmental law experts have questioned the agency's logic given what they say is already known about the dangers of air pollution, and in light of a new study linking long-term exposure to coronavirus deaths.

Two weeks before the EPA's proposal, a Harvard study found that even a small increase in this type of microscopic air pollution is associated with an 8% increase in the Covid-19 death rate. The study also found that people living in counties where there is long-term exposure to air pollution are more likely to die from Covid-19.

"It's a stunning decision by the EPA, but one can't say that it's unexpected, only because this administration has made several of these," said Richard Lazarus, a professor of environmental law at Harvard Law School.

That study has not yet been peer-reviewed, and, according to The New York Times, the EPA did not factor the findings into its PM 2.5 analysis because the review of the rule had mostly been completed when the study published.

In response to questions about the findings, an EPA spokesperson said, "The study's authors have miscalculated our guidance and are also making false assumptions about our NAAQS proposal," and that PM 2.5 levels in the US have fallen substantially in the past decade.

However, the study's lead author says the EPA's move does not seem to take into account what we already know about Covid-19 -- and air pollution in general.

"Regardless of what my study is saying and whether to trust my science, I do think it's unwise to roll back regulatory pollution standards at a time when we know there is a virus that is attacking the lungs," said Francesca Dominici, a Harvard biostatistician and the lead author of the study on links between particle pollution and Covid-19.

Dominici says there is also a need for more investigation of the impacts of air pollution and Covid-19 on minority communities.

The EPA's own proposed rule on this type of air pollution acknowledges that "there is consistent evidence across multiple studies demonstrating an increase in risk for nonwhite populations."

Evidence shows that in the US, minorities often breathe more polluted air than white people, and that those same groups have been hit hardest by the pandemic.

"I'm not saying that [air pollution] is the only factor, but I think that's an angle that should be investigated more," Dominici said.

New mercury rule is a 'shot across the bow'

In April, the EPA made another major policy move, when it changed how it evaluates regulations on emissions of mercury and other toxic metals coming from coal and oil-fired power plants.

Mercury in the air can contaminate water and severely damage the nervous systems of those who ingest it, with pregnant women and children facing the greatest risk.

Though the new rule does not change how much mercury power plants can emit, it does change how the agency calculates the costs and benefits of forcing power generators to comply.

In its new cost analysis, the EPA found that the costs of limiting these hazardous pollutants -- estimated at between $7.4 billion and $9.6 billion annually -- now outweigh the benefits.

In a statement announcing the new findings, Wheeler said, "Under this action, no more mercury will be emitted into the air than before," and that the agency's move was correcting the previous administration's "flawed" findings.

But Lazarus says this could have big consequences when it comes to how the agency regulates other pollutants, and could open existing rules up to challenges in the courts.

"They're indicating that they're going to measure costs and benefits in a very narrow way, which will reduce the level of benefit calculated as compared to the costs," Lazarus said. "In future rulemaking, it will be harder to justify tougher hazardous air-pollution standards under the Clean Air Act."

He says that even though the current mercury standard was left unchanged, the policy sends a powerful signal to companies that might be eager to challenge other regulations.

"It's a shot across the bow that is likely to weaken standards in the future, and may make these mercury standards more vulnerable to attack in the courts by industry."