Category Archives: Air pollution

Proposed EPA rule would disadvantage minority communities

[Editor: The excellent article below does not link to the EPA’s proposed new rule.  It can be found here, and note that PUBLIC COMMENTS may be sent on or before July 27, 2020.  Submit your comment here.  – R.S.]

Soot rule thrusts EPA into spotlight on race

E&E News, by Jean Chemnick, June 12, 2020
Louisiana refinery. Photo credit:  John Dooley/Sipa Press/Newscom
A refinery is seen near Venice, La. EPA is changing its cost-benefit analysis to discount the health savings from lower levels of particulate matter and other pollutants. John Dooley/Sipa Press/Newscom

EPA published a proposal in the Federal Register yesterday that critics described as an assault on minority communities coping with the public health legacy of structural racism.

The agency’s plan would mandate changes to the way future rules under the Clean Air Act would weigh the costs and benefits of climate and air pollution regulations.

It’s the first time EPA has attempted such a rulemaking, and critics say the goal is to saddle future administrations with an inflexible set of cost-benefit methodologies that discount benefits from cutting pollutants while stressing cost to industry.

The rule would also bar EPA from giving special consideration to individual communities that bear the brunt of environmental risks — frequently populations of color.

“The rule won’t take into account any benefit that can’t be monetized and quantified, including important things like the effect, say, of a mercury rule on tribal communities that rely on fish and wildlife that are contaminated with mercury or the effect of particulate matter on communities of color and disadvantaged folks who live near the power plants that are being controlled,” said Ann Weeks, legal director of the Clean Air Task Force.

The Obama EPA did give special weight to the benefits that would accrue to specific communities when assessing whether a rule was cost-effective, she said. But this proposal seeks to make that impossible.

“You basically are tying your own hands, if you’re the agency, by saying this is the way you have to do things,” she said.

EPA describes the draft rule as an effort to improve transparency by demanding a strict accounting of costs and benefits for all economically significant air quality and climate change rulemakings promulgated under the landmark environmental law.

But it raises questions about whether a future administration could count so-called co-benefits when drafting regulations. Co-benefits are reductions in pollutants that aren’t the rule’s primary target but that yield public health benefits that EPA has traditionally counted.

Administrator Andrew Wheeler, a former energy lawyer, has long sought to sideline co-benefits, which industry sees as justifying rules whose costs outweigh true environmental benefits.

The co-benefit that has packed the greatest punch in past Clean Air Act rulemakings is fine particulate matter, or soot. Epidemiological studies are chock-full of data linking these tiny particles to pulmonary, respiratory and neurological ailments and death.

So demonstrating that a rule would reduce particulate matter adds to its value — a fact that even the Trump EPA used last year to show that its Affordable Clean Energy rule for power plant carbon dioxide was worth its costs.

‘History of racism’

The proposal comes as communities of color are experiencing some of the worst impacts of the coronavirus, while protests over racism and police brutality continue in cities across the country.

There’s evidence that elevated exposure to soot from highways, industrial facilities and incinerators that have for decades been built in predominantly black, Latino and Asian American communities are disproportionately harming the health of their residents.

“It’s all deeply ingrained in the history of racism and the history of civil rights,” said Sofia Owen, a staff attorney with Alternatives for Community & Environment, an environmental justice group based in Boston. “The siting of these facilities — where our highways are, where incinerators are, where compressor stations or the bus depots and the train depots are — is communities of color and low-income communities.”

The Union of Concerned Scientists released modeling last year showing that Asian Americans are, on average, exposed to particulate matter concentrations from vehicle tailpipes that are 34% higher compared with other Americans.

They weren’t alone. Soot exposure was 24% higher for African Americans and 23% higher for Latinos. White Americans are exposed to 14% less soot from tailpipes than the average American (Greenwire, June 27, 2019).

“It’s primarily the PM2.5 that is responsible for environmental damage and health damage in communities living near highways,” said Maria Cecilia Pinto de Moura, a senior vehicles engineer with UCS, referring to particulate matter 2.5 micrometers or less in diameter. The science advocacy group is now doing similar modeling on proximity to coal-fired power plants by demographic group, she said.

The health impacts of PM2.5 exposure can be severe.

A 2017 study by researchers at the Harvard T.H. Chan School of Public Health and other institutions found that incremental increases in soot exposure below the standards set by EPA can result in significantly more deaths among senior citizens. The study found that black people were three times more likely to die from soot exposure than other Americans.

“We know that when you inhale fine particulate matter, they penetrate very deep into your lungs, and they can actually get into your bloodstream, and they initiate a form of inflammation that can cause pneumonia and cardiovascular disease,” said Francesca Dominici, a professor of biostatistics at the School of Public Health and an author of the 2017 study.

Dominici also co-authored a recent study showing that counties with higher levels of particulate matter experienced more deaths related to COVID-19, the disease caused by the novel coronavirus (Greenwire, April 7).

There’s a link between particulate matter and acute respiratory distress syndrome, she said, which causes COVID-19-related deaths.

“If you’re living in a county and you’re breathing polluted air for a very long time, even absent COVID, we know that your lungs are inflamed,” Dominici said. “After you contract COVID, your ability to respond to the inflammatory nature of COVID is severely compromised because your lungs already have inflammation.”

The result is worse for black and Latino people who contract COVID-19. The Centers for Disease Control and Prevention reported in April that 33% of those hospitalized with the disease were black, as were nearly a quarter of those who died. Eighteen percent of the U.S. population is black.

While racial minorities are more impacted by high soot levels, they’re also responsible for producing less of it.

A 2019 study published in the Proceedings of the National Academy of Sciences found that non-Hispanic whites consume the majority of the goods and services responsible for particulate matter. Black and Latino people on average are exposed to 56% and 63% more soot, respectively, than is linked to their consumption.

The same study estimated that soot caused 131,000 premature American deaths in 2015.

“The long tail of this is that particularly black Americans and Latinx communities have been discriminated against in this country, and because of their poverty, they are forced to live in neighborhoods that are less expensive and more polluted,” said Aaron Bernstein, director of the Harvard Chan School’s Center for Climate, Health and the Global Environment.

EPA’s cost-benefit exercises could consider that history of racial injustice when assessing whether a rule is warranted, he noted.

“If you clean up the air, there is a pretty good likelihood that we’re going to benefit people of color more. And should we in fact prioritize those actions because of historical and, frankly, present-day injustices?” he said. “That is a highly contentious arena right now, but it’s hard to ignore, given what’s going on.”

Progress

The gap between soot exposure levels of white and nonwhite Americans has actually been shrinking in recent years.

A paper released in January that used satellite-based measurements to track air quality across the country found that disparities between soot levels in predominantly minority and white areas fell by nearly two-thirds between 2000 and 2015.

Reed Walker, an associate professor of economics at the University of California, Berkeley, and one of the authors of the study, said this was partly due to white people moving into cities and minorities heading to the suburbs.

But a much larger part of the story, he said, had to do with the Clean Air Act.

Particulate matter standards set under the law — current ones were implemented in 2005 — require counties that fail to meet National Ambient Air Quality Standards to take aggressive action to reach attainment.

“It just so happens that African Americans are overrepresented in these dirty areas,” Walker said, noting that in the last 15 years, counties with large minority populations have reduced particulate matter more than predominantly white counties.

Still, research shows that soot can cause illness and death at levels below federal air quality standards. This year, EPA declined to tighten the standard despite public health advocates’ warnings that an update is long overdue.

And the proposed cost-benefit rule seems to be directed at making tougher rules harder to promulgate in the future.

“Any failure to tighten the standard is going to continue the disproportionate exposures faced by individuals in those communities,” Walker said.

This story also appears today in Climatewire.

Emissions are way down. No, that’s not all good news for the environment.

Chaos in the oil sector could actually intensify climate change.

Mother Jones, by Rebecca Leber, April 21, 2020
Getty

As the coronavirus cripples world economies, greenhouse gas emissions are plummeting: This year, they could drop by as much as 5.5 percent—the largest decrease ever recorded. On Monday, the price of oil went negative, meaning storing oil now costs more than the oil itself. Since we’re burning less gas and fuel, air pollution has dropped 30 percent in northeastern cities, and Los Angeles’ notorious smoggy skyline has cleared.

You might be thinking all this is great news for the environment. It’s a nice idea—but the real story is more complicated. “You don’t want companies collapsing like this,” says Andrew Logan, oil and gas director of Ceres, a think tank focused on sustainable investment. “Even the most ardent climate advocate shouldn’t wish for a chaotic transition in this sector. A chaotic transition brings all sort of pain to workers and also the environment.”

It helps to think of COVID-19 as a test run—a very painful one—of what an industry in decline will look like. “We’re seeing, as is case the now, what the cliff looks like if everyone shuts down at the same time,” Logan says.

With a glut of supply, North America producers Exxon, Shell, Devon Energy, and Cenovus Energy have already collectively announced spending cuts this year totaling $50 billion, according to the Wall Street Journal. In North Dakota, Trump donor Harold Hamm’s Continental Resources drilling company has cut output by 30 percent the next two months. In Canada, the famously destructive tar sands are too expensive to mine and refine on oil prices this cheap. Even the Southwest’s Permian Basin, the most productive region for oil and gas in the United States, is expected to see dramatic closures.

Environmentalists are worried about what comes next, because of the many unintended consequences of market chaos. For starters, when gas prices tank, Americans will likely start buying more cars and taking more road trips, driving up demand all over again.

Other environmental problems aren’t quite so obvious. Lorne Stockman, a senior research analyst with the climate advocacy group Oil Change International, worries that the coming bankruptcies this year “are an environmental nightmare in the making,” with “wells left to rot as bankruptcy proceedings are going through.”

As the industry contracts, some drilling operations will simply leave their wells, and many don’t have the funding set aside to take proper precautions to make sure greenhouse gases and other pollutants don’t leak out. Environmental advocates are especially worried about leaks of methane, a particularly potent greenhouse gas.

Abandoned wells are already a big problem. Even in relatively good times, oil and gas wells still dry up. When they do, they might be sold to smaller, sometimes less scrupulous operators to tap what’s left in the well. Then those operators eventually abandon the well or go bankrupt. They can’t afford to clean up the site, which involves plugging the well with cement to avoid leaks into groundwater.

We don’t know for sure how many of these wells exist around the country, though the EPA estimates there are more than 1.5 million of them that have accumulated over a century. Wyoming has had thousands it’s in the process of plugging, and Pennsylvania has 8,000. Taxpayers will eventually pay for both cleanup and environmental damages.

Drilling operations that don’t shutter will have to find ways to cut costs. In boom times, methane is valuable to drillers because it can be captured and reused for fuel. But when oil and natural gas prices have crashed in the past, drillers have sought to get rid of excess methane in the cheapest way possible—by burning it (a process known as “flaring”) or simply letting it leak into the atmosphere (called “venting”). Both processes can contribute to climate change and contaminate surrounding communities. Flaring and venting worry many environmental advocates. The International Energy Agency notes that “low natural gas prices may lead to increases in flaring or venting, and regulatory oversight of oil and gas operations could be scaled back.”

Methane emissions hit a 20-year high last year, according to the National Oceanic and Atmospheric Administration. Although scientists don’t fully understand why, they believe that fracking operations may dramatically underestimate the methane they release. According to the Environmental Defense Fund, operations typically lose 15 times the rate that producers report because of malfunctions and intentional venting. The COVID-19 crisis could lead to more leaks, because companies won’t have any incentive to capture methane to use for fuel.

Amid the turbulence in the oil sector, the Trump administration has continued to roll back environmental regulations, and it has already undone Obama-era rules targeting methane emissions from oil and gas operations.

Nathalie Eddy, a field advocate for the environmental watchdog Earthworks, is worried that environmental contamination will be made worse as the administration weakens rules. “When the market falls like this one of the first things that will go is the limited capacity for inspection,” she says. The EPA, Department of the Interior, and Department of Transportation have already announced they will suspend some routine inspections and monitoring, including pipeline reporting and field inspections, and waive civil penalties if violators say COVID-19 was a factor.

Climate advocates have urged the EPA and Department of the Interior to require companies to monitor methane leaks and set aside money for their cleanup. To help the sector recoup the lost revenue, they propose a job stimulus program aimed at reclaiming these sites for the double-duty benefit of a clean environment and keeping workers employed.

But so far, those pleas are going unanswered. The Trump administration has floated several schemes for helping the oil sector: During the first round of stimulus, congressional Democrats managed to shoot down the oil industry’s bailout request. Now, the administration is considering paying producers to leave crude in the ground until the global glut shrinks. Meanwhile, the major banks want some collateral for the $200 billion they are owed from oil companies: According to Reuters, JPMorgan Chase, Wells Fargo, Bank of America, and Citigroup could even seize the industry’s assets, which could pose an enormous conflict of interest for a financial sector that just months ago was signaling a move away from the oil sector.

So far, it looks like the short-term emissions drop won’t result in any lasting policy improvements, Stockman says. “We have seen the wrong kind of stimulus that isn’t aimed at changing our relationship to fossil fuels.”

What Just Happened to the Mercury Rule?

Energy Institute Blog, by Meredith Fowlie, April 20, 2020

Last week’s EPA decision adds insult to injury for our already vulnerable communities.

Perhaps you missed it. There’s a lot going on right now. But amidst all the COVID-19 headlines last week, the EPA decided that it is not “appropriate and necessary” for the government to limit emissions of mercury and other hazardous air pollutants from power plants.

coal
Source: Pixabay

This is not a roll-back of a regulation. It’s more nuanced than that. It’s a high-stakes procedural move with two important implications:

First, it scraps the legal basis for the Mercury and Air Toxics Standards (MATS) which limit hazardous air pollution from coal and oil-fired power plants. Having knocked the legal foundations out from under this important regulation, I think there’s a real risk that power plants will find ways to dial back on compliance in the future.

Second, it sets a dangerous precedent for how the benefits and costs of federal environmental regulations are assessed. The ruling removes significant health benefits from cost-benefit consideration on the grounds that they are not directly targeted by MATS.

This announcement comes at a time when the country is reeling from the global coronavirus pandemic. Protecting public health is top of mind. We’ve all become keenly aware of how actions we take can indirectly protect the health of the most vulnerable among us. With these benefits in mind, we are taking action.

Meanwhile, the EPA has decided that the indirect health benefits of pollution reductions should not be considered in regulatory cost-benefit analysis. This decision departs recklessly from standard practices for responsible public decision-making.

Some colleagues and I recently published this paper (based on our longer report) which points out deep flaws in this EPA decision. The agency’s own Science Advisory Board released a report calling for a “do-over”. Hundreds of thousands of public comments raise concerns. Even the electricity sector stands in opposition. The Trump EPA response: To hell with it. We are pushing ahead.

To understand what this means, we need to remember how we got here.

The Mercury and Air Toxics Standards limits the emissions of mercury and other hazardous air pollutants (HAPs) from power plants. To justify the rule, the EPA must demonstrate that it is appropriate and necessary. Back in 2011, the EPA supported this argument with a detailed analysis that projected big public health benefits from the power plant emissions reductions expected under the regulation. The table below, taken from the 2011 analysis, shows monetized benefits far exceeding the costs.

table
Summary of the quantified benefits and costs in the 2011 RIA for the MATS rule. These are projected for the year 2016. The data reported in this table are from Table ES-1 of EPA (2011).

There were some serious bumps on the road to implementation. But power plants began complying in 2016. The industry has since invested billions to install pollution abatement equipment in order to meet MATS requirements.

Last year, the Trump EPA started working to reverse the appropriate and necessary finding. The agency issued this six-page memo that re-interprets the 2011 cost-benefit analysis. There’s no new information here. The big change is that the “co-benefits” – health benefits that result indirectly from MATS compliance—have been wiped off the cost-benefit board. If we ignore these benefits (row 3 in the table above), MATS appears to fail the cost-benefit test.

There are many reasons to be concerned about this maneuver.  Let me unpack three:

  1. Co-benefits are real benefits

When power plants reduce mercury emissions, they also reduce emissions of precursors to harmful particulate matter (PM). Reducing exposure to small particulates saves lives. These benefits are referred to as “co-benefits” because they are caused by – but not directly targeted by – the regulation.

If a policy will generate big health benefits, directly or indirectly, these should be counted. Federal agencies are under Executive Order to weigh the available evidence on all significant costs and benefits in their regulatory assessments. This is also required under the EPA’s own guidelines for economic analysis.

An official decision that eliminates or reduces consideration of co-benefits sets a troubling precedent for future regulatory decisions. If this approach becomes standard, it becomes much more difficult for the EPA to justify socially beneficial regulations. Greenhouse gas emissions regulations- which can deliver significant reductions in local air pollution- are one important example.

  1. Direct benefits estimates are outdated and incomplete

The 2011 direct benefit projections that serve as a basis for last week’s decision reflect only one health benefit from reducing mercury emissions: improvements in the IQs of children whose families catch and eat freshwater fish. This narrow focus explains why those 2011 direct benefits estimates are so small.

A decade later, we know a lot more about how power-plant mercury accumulates in commercial seafood consumed by many Americans. In addition, recent research suggests that mercury exposure could cause cardiovascular problems. If these additional health impacts were accounted for, the direct benefits of HAP reductions would look quite different. But the 2020 EPA decision is still referencing outdated and incomplete 2011 benefits numbers.

  1. Costs are largely in the past

To comply with MATS, billions have been invested in equipment that scrubs harmful pollution out of power plant emissions. In other words, the investment costs that comprise the majority of the 2011 cost projections have already been incurred. Going forward, the costs we need to consider are the costs of operating this pollution abatement equipment. Estimates I’ve seen range from  $1.80/MWh to as high as $7.92/MWh (a non-trivial increase in coal-fired electricity generation costs).

FGD
Flue gas desulfurization is one of the technologies used to comply with MATS (Source)

By dismissing the legal basis for the rule, MATS is left wide open to the challenge that the pollution controls are no longer legally required. If I were a coal plant operator, I might read between the lines of this decision and conclude that the EPA is not so concerned about enforcing MATS going forward.

Coal plants across the U.S. are struggling to compete with natural gas and renewables. If MATS requirements are not there to keep pollution controls switched on, plants in competitive electricity markets will have an incentive to turn this equipment off to save a few dollars/MWh. If this happens, downwind communities will pay a hefty health price.

Adding insult to injury

You would think that a high-stakes regulatory decision like this would merit an analysis update given that almost a decade has passed since the original assessment was done. The reams of data and scientific evidence that have accumulated since 2011 could provide a much more accurate evaluation of the rule’s benefits and costs, in addition to a more informed basis for re-evaluating the appropriate and necessary finding.  Instead, this EPA has dusted off a stale 2011 analysis, deleted the co-benefits, and declared the rule unnecessary and/or inappropriate.

The timing of this decision feels particularly callous because the communities that have historically been most exposed to high levels of air pollution are the ones being hit hardest by the COVID-19 crisis. This recent study suggests that even small increases in long-term exposure to particulate matter significantly increase COVID-19 fatality risk.

The Trump administration assures us it is putting “safety first” during this COVID-19 epidemic. But in the background, Trump appointees have been doing quite the opposite with decision after decision after decision. This MATS reversal has the potential to do real damage. But if there is good news to be found in this story, it’s that it will take time to play out. One more reason to work hard to course correct in November.

Keep up with Energy Institute blogs, research, and events on Twitter @energyathaas

Suggested citation: Fowlie, Meredith. “What Just Happened to the Mercury Rule?” Energy Institute Blog, UC Berkeley, April 20, 2020, https://energyathaas.wordpress.com/2020/04/20/what-just-happened-to-the-mercury-rule/

E.P.A. Plans to Get Thousands of Deaths Off the Books by Changing Its Math

By Lisa Friedman, New York Times, May 20, 2019
The Hunter power plant in Castle Dale, Utah, which burns an estimated 4.5 million tons of coal a year.  Credit: Brandon Thibodeaux for The New York Times

WASHINGTON — The Environmental Protection Agency plans to change the way it calculates the future health risks of air pollution, a shift that would predict thousands of fewer deaths and would help justify the planned rollback of a key climate change measure, according to five people with knowledge of the agency’s plans.

The proposed change would dramatically reduce the 1,400 additional premature deaths per year that the E.P.A. had initially forecast as a result of eliminating the old climate change regulation — the Clean Power Plan, which was President Barack Obama’s signature climate change measure. It would also make it easier for the administration to defend its replacement, known as the Affordable Clean Energy rule.

It has been a constant struggle for the E.P.A. to demonstrate, as it is normally expected to do, that society will see more benefits than costs from major regulatory changes. The new modeling method, which experts said has never been peer-reviewed and is not scientifically sound, would most likely be used by the Trump administration to defend further rollbacks of air pollution rules.

It is not uncommon for a presidential administration to use accounting changes to make its regulatory decisions look better than the rules of its predecessors. But the proposed new modeling method is unusual because it relies on unfounded medical assumptions and discards more than a decade of peer-reviewed E.P.A. methods for understanding the health hazards linked to the fine particulate matter produced by burning fossil fuels.

Fine particulate matter — the tiny, deadly particles that can penetrate deep into the lungs and enter the bloodstream — is linked heart attacks, strokes and respiratory disease.

The five people familiar with the plan, who are all current or former E.P.A. officials, said the new modeling method would be used in the agency’s analysis of the final version of the ACE rule, which is expected to be made public in June. William L. Wehrum, the E.P.A. air quality chief, acknowledged in an interview the new method would be included in the agency’s final analysis of the rule.

The new methodology would assume there is little or no health benefit to making the air any cleaner than what the law requires. On paper, that would translate into far fewer premature deaths from air pollution, even if it increased. The problem is, scientists say, in the real world there are no safe levels of fine particulate pollution in the air.

“Particulate matter is extremely harmful and it leads to a large number of premature deaths,” said Richard L. Revesz, an expert in environmental law at New York University. He called the expected change a “monumental departure” from the approach both Republican and Democratic E.P.A. leaders have used over the past several decades and predicted that it would lay the groundwork for weakening more environmental regulations.

“It could be an enormously significant impact,” Mr. Revesz said.

The Obama administration had sought to reduce planet-warming greenhouse gas emissions under the Clean Power Plan by pushing utilities to switch away from coal and instead use natural gas or renewable energy to generate electricity. The Obama plan would also have what’s known as a co-benefit: levels of fine particulate matter would fall.

The Trump administration has moved to repeal the Obama-era plan and replace it with the ACE rule, which would slightly improve the efficiency of coal plants. It would also allow older coal plants to remain in operation longer and result in an increase of particulate matter.

Particulate matter comes in various sizes. The greatest health risk comes from what is known as PM 2.5, the range of fine particles that are less than 2.5 microns in diameter. That is about one-thirtieth the width of a human hair.

The E.P.A. has set the safety threshold for PM 2.5 at a yearly average of 12 micrograms per cubic meter. While individual days vary, with some higher, an annual average at or below that level, known as the particulate matter standard, is considered safe. However, the agency still weighs health hazards that occur in the safe range when it analyzes new regulations.

Industry has long questioned that system. After all, fossil fuel advocates ask, why should the E.P.A. search for health dangers, and, ultimately, impose costs on industry, in situations where air is officially considered safe?

Mr. Wehrum, who worked as a lawyer and lobbyist for chemical manufacturers and fossil fuel businesses before moving to the E.P.A., echoed that position in the interview. He noted that, in some regulations, the benefits of reduced particulate matter have been estimated to total in the range of $40 billion.

“How in the world can you get $30 or $40 billion of benefit to public health when most of that is attributable to reductions in areas that already meet a health-based standard,” he said. “That doesn’t make any sense.”

William L. Wehrum, the E.P.A. assistant administrator for air and radiation. Credit: Ron Sachs/CNP/MediaPunch

Mr. Wehrum confirmed that he had asked his staff to study the issue and that the final version of the ACE rule would include a variety of analyses, including one that does not take into consideration health effects below the particulate matter standard. He acknowledged that doing so would reduce the 1,400 premature deaths the agency had initially predicted as a result of the measure.

He called the attention given to that initial forecast “unfortunate” and said the agency had included the figure in its analysis to show the varied results that can be achieved based on different assumptions.

Mr. Wehrum said the analyses the agency is conducting “illuminate the issue” of particulate matter and the question of what level is acceptable for the purposes of policymaking. He said new approaches would allow for public debate to move ahead and that any new methods would be subject to peer review if they became the agency’s primary tool for measuring health risks.

“This isn’t just something I’m cooking up here in my fifth-floor office in Washington,” Mr. Wehrum said.

Roger O. McClellan, who has served on E.P.A. advisory boards and as president of the Chemical Industry Institute of Toxicology, an industry-financed research center, said the data for health risks below the particulate matter standard was weak and that he did not accept the argument that agencies must calculate risk “down to the first molecule of exposure.”

“These kinds of approaches — that every molecule, every ionization, carries with it an associated calculable health risk — are just misleading,” Mr. McClellan said.

To put the matter in perspective, most scientists say particulate matter standards are like speed limits. On many highways, a limit of 65 miles per hour is considered reasonable to protect public safety. But that doesn’t mean the risk of an accident disappears at 55 m.p.h., or even 25.

Jonathan M. Samet, a pulmonary disease specialist who is dean of the Colorado School of Public Health, said the most recent studies showed negative health effects well below the 12-microgram standard. “It’s not a hard stop where we can say ‘below that, air is safe.’ That would not be supported by the scientific evidence,” Dr. Samet said. “It would be very nice for public health if things worked that way, but they don’t seem to.”

Daniel S. Greenbaum, president of the Health Effects Institute, a nonprofit research organization that is funded by the E.P.A. and industry groups, acknowledged there was uncertainty around the effects of fine particulate matter exposure below the standard.

He said it was reasonable of the Trump administration to study the issue, but he questioned moving ahead with a new system before those studies are in. “To move away from the way this has been done without the benefit of this full scientific peer review is unfortunate,” he said.


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Lisa Friedman reports on climate and environmental policy in Washington. A former editor at Climatewire, she has covered nine international climate talks. @LFFriedman