EPA Retains Soot Standards; Drastic PM Reductions Already Achieved, Industry Says

In a significant but controversial final action, the Environmental Protection Agency (EPA) on Dec. 7 retained its existing National Ambient Air Quality Standards (NAAQS) for both fine and coarse particulate matter (PM2.5 and PM10).

While the EPA said the decision came “after careful review and consideration of the most recent available scientific evidence and technical information, consultation with the agency’s independent scientific advisors, and consideration of more than 60,000 public comments on the proposal,” environmental groups largely viewed the action as a dereliction of the agency’s regulatory duty.

The power sector, meanwhile, supported the measure, underscoring its success at slashing PM and precursor air pollutant emissions and pointing to future reductions from electrification of the transportation and industrial sectors. 

Why the Final Action Is Notable

Fine particles (PM2.5), which are 2.5 micrometers in diameter and smaller, are emitted by a variety of sources, including smokestacks, vehicles, and fires, but they also form when gases emitted by power plants, other industrial processes, and gasoline and diesel engines react in the atmosphere. Coarse particles (PM10), which have diameters between 2.5 and 10 micrometers, include road dust kicked up by traffic, some agricultural operations, construction and demolition operations, industrial processes and biomass combustion. 

The Clean Air Act (CAA) requires the EPA to set two types of NAAQS for PM: primary standards to protect public health “with an adequate margin of safety,” and secondary standards to protect public welfare from both known and anticipated adverse effects, including from haze in cities and national parks. Under the law, the EPA must review the NAAQS every five years to determine whether they should be retained or revised. Since 1971, the agency has regulated PM pollution four times—in 1987, 1997, 2006, and 2012. 

In 2012, the Obama administration tightened the primary standard for PM2.5 to 12.0 micrograms per cubic meter (µg/m³) from the existing 1997-set annual standard of 15.0 μg/m³, but it retained the 2006-issued 24-hour primary fine particle standard of 35 μg/m³. On Monday, the EPA retained both the annual and 24-hour standards for PM2.5. It also retained the existing 24-hour primary and secondary standards (which are identical) for PM10 at its 1987-set level of 150 µg/m³. The EPA also said on Monday it is addressing the ecological effects associated with PM in a separate review of the secondary NAAQS for oxides of nitrogen, oxides of sulfur, and PM. 

For all these standards, the level generally means a regulated area meets the standard if it does not exceed the level on average over a three-year period. Under President Trump, however, the EPA has redesignated 57 nonattainment areas to attainment with standards for six key criteria air pollutants: carbon monoxide, ground-level ozone, lead, nitrogen oxides, PM, and sulfur oxides. This includes nine areas for PM2.5 and 12 areas for PM10. In October, for example, the EPA declared that West Virginia meets all current air quality standards after the approval of the redesignation of Marshall County.

The EPA says the redesignations “mean cleaner air, improved health outcomes, and greater economic opportunities for cities and communities across the country,” but the action has been a key sticking point for environmental groups, which suggest the EPA has granted industry reprieves without adequate emphasis on their environmental implications.

In a statement to POWER on Monday, EPA Administrator Andrew Wheeler said that in abiding with existing standards, the nation has already lowered its PM levels to “well below” those of its global competitors. The EPA said PM2.5 levels are “approximately five times below the global average, six times below Chinese levels, and 20% lower than France, Germany, and Great Britain. Between 2000 and 2019, average PM2.5 concentrations in the U.S. fell by 44% and average PM10 concentrations similarly fell by 46%.”

Industry: Power Plant PM Emissions Fell 96% Since 1990

According to the Edison Electric Institute (EEI)—a trade organization that represents all U.S. investor-owned power companies—power industry PM2.5 and other key air pollutant emissions have fallen by 90% since 1990. Responding to the EPA’s April 2020 proposed rule to retain the standards, the group told the EPA on June 29 that part of that decline is rooted in a “profound, long-term transformation in how electricity is generated, transmitted, and used.” The transformation is being driven by “low and declining costs for natural gas and renewable energy resources, technological improvements, changing customer expectations, federal and state regulations and policies, and the increasing use of distributed energy resources.” 

However, the EEI also highlighted stringent PM2.5 pollution controls installed at existing power generating units, such as fabric filters and electrostatic precipitators. “The most important electric power emissions related to PM2.5 are sulfur dioxide (SO₂) and nitrogen oxides (NO_x), which can serve as precursors to formation of PM2.5. Electric power sector emissions of SO₂ and NO_x are reduced by 94% and 86%, respectively, over the period 1990 to 2019,” it said. Industry has also reduced its mercury emissions by about 86% from 2010 to 2017, and emissions of both acid gases and of total hazardous air pollutants have fallen by 96%, it said. “As a result of these emissions reductions and those from other types of emissions sources, EPA reports a 43% decrease in PM2.5 concentrations over the period of 2000–2019, averaged over more than 400 monitoring sites.” 

Industry “is committed to achieve even more,” EEI said. “Collectively, EEI’s member companies are on a path to reduce carbon emissions 50% by 2030 using a combination of replacing coal with natural gas-based generation, energy efficiency, and deployment of new renewable energy, especially wind and solar. These technologies will enable significant, cost-effective carbon reductions as well as continue to reduce PM2.5, SO₂ and NO_x emissions.” 

The power sector, meanwhile, is building infrastructure needed to support increased electrification of multiple sectors, an effort that could remove emissions from transportation and industrial sectors. “As EPA looks forward to implementing the PM2.5 NAAQS, the Agency should provide the states and industry with significant regulatory flexibility to allow for states and sources to leverage these advances,” it said. Actions the agency could take include incorporating an electrification policies roadmap that addresses how the EPA’s on-road model “MOtor Vehicle Emission Simulator (MOVES)” can account for electric vehicles in the on-road fleet when modeling emissions for state and tribal implementation purposes. 

Environmental Groups: Soot Decision ‘Dangerous’ 

The EPA’s action to retain the PM NAAQS standard prompted immediate reaction from a number of environmental groups, which garnered widespread media coverage. Nonprofit global organization the Environmental Defense Fund (EDF) pointed to health implications for communities in close proximity to industrial sources, calling on the incoming Biden-Harris administration to immediately “reverse this harmful decision.” EDF noted Wheeler had disbanded a 26-member PM expert panel. “A smaller, divided advisory panel made up mostly of Wheeler’s appointees then rejected the expert advice and recommended leaving the soot standards at their current levels.”

At least one power company, Georgia-based electric cooperative Oglethorpe Power Corp., opined on these allegations. “EPA has completed a thorough review and assessment of the science that included the Agency giving careful consideration to the scientific advice of [the EPA’s Clean Air Scientific Advisory Committee (CASAC)] and providing extensive and complete responses to all of the comments and recommendations received from CASAC,” wrote Craig Jones, Oglethorpe Power’s director of Environmental Policy, in June. The EPA prepared an Integrated Scientific Assessment that provides a comprehensive and systematic technical assessment of the available science relevant to understanding the public health and welfare impacts of ambient air exposures of PM, he said, but the agency went even “further than statute” by also preparing a policy assessment in support of its review of the PM NAAQS. 

“EPA’s proposal to retain the current PM NAAQS without revision is consistent with CASAC’s recommendations, well-reasoned, and scientifically sound. This is clearly evidenced in the preamble to the Proposal, which provides a comprehensive discussion of the NAAQS review process, detailed information on emission characteristics of PM and PM precursors (i.e., sulfur dioxide and nitrogen dioxide), and extensive technical analyses of the uncertainties on public health and welfare effects, including exposure-measurement error and a detailed explanation of how these uncertainties affected EPA’s risk assessment,” he explained.

While the CASAC was unable to ultimately reach a “consensus agreement” on the annual PM2.5 NAAQS, “where there is substantial disagreement on the science, the CAA delegates to EPA the authority to make the appropriate public health policy judgment on where to set ambient air quality standard,” wrote Jones. 

—Sonal Patel is a POWER senior associate editor (@sonalcpatel, @POWERmagazine).