On March 6, 2024, the U.S. Environmental Protection Agency (EPA) promulgated revised National Ambient Air Quality Standards (NAAQS) for particulate matter (PM). The final rule was signed on Feb. 7, 2024. New NAAQS standards are always controversial, and this one is no exception.
The EPA lowered the primary annual fine particulate matter (2.5 micrometers (μm) or less in diameter) (PM2.5) standard from 12.0 μg/m3 to 9.0 μg/m3. The EPA retained the current primary 24-hr PM2.5 standard and the current primary 24-hr PM10 standard and also retained the current secondary 24-hr PM2.5 standard, secondary annual PM2.5 standard, and secondary 24-hr PM10 standard.
Public health stakeholders cheered, but certain others questioned the new values. Detractors claim the data for which the new annual PM2.5 standard relies is questionable and also cite higher compliance costs.
Background
The Clean Air Act (CAA) requires the EPA to issue NAAQSs for certain listed pollutants and to review those standards every five years. PM, a mixture of solid particles and liquid droplets found in the atmosphere, is among the pollutants. The size of these particles varies greatly, ranging from tiny particles to larger particles, like soot. PM, especially PM2.5 (so-called fine particulate), has been associated with adverse human health effects, including asthma, bronchitis, cardiovascular disease, premature death, and adverse environmental impacts, including haze formation and other ecological effects.
The EPA established a 24-hour and annual standard for PM. As noted, the agency also established separate standards for PM based on particle size. PM2.5 includes particles 2.5 μm or less in diameter and is referred to as fine particulate. PM10 is larger and includes particles less than or equal to 10 μm in diameter. Both particle sizes are inhalable.
The EPA completed its review of the PM NAAQS in 2020 and decided to retain the primary and secondary NAAQS without revision. This elicited several petitions filed in federal court seeking reconsideration of the EPA’s decision. Stakeholders argued new information on health effects warranted reevaluation of the primary PM2.5 standard and claimed the data indicated a level below the then-current level of PM2.5 12.0 μg/m3 was justified.
In January 2023, the EPA proposed altering the PM2.5 annual NAAQS. The proposal would lower the PM2.5 annual NAAQS allowable limit to a value between 9.0 and 10.0 μg/m3 and to maintain the current primary and secondary 24-hr PM2.5 standard. The EPA also sought comment on other aspects of the NAAQS, including certain monitoring requirements, data calculations and PM monitoring methods, among other issues. The EPA also sought comment on an alternative annual standard from 8.0 μg/m3 to 11.0 μg/m3.
The EPA prepared cost estimates for the revised standard in the form of a regulatory impact analysis (RIA). The RIA projected significant improvement in public health by documenting reduced human adverse health effects among the general population and especially among susceptible subpopulations, including infants, children, the elderly and people afflicted with asthma.
The EPA quantified the number and economic value of the estimated premature deaths and illnesses associated with PM that could be avoided or diminished with the proposed PM2.5 annual standard of between 9.0 and 10.0 μg/m3. The RIA predicted a revised PM NAAQS of 9.0 μg/m3 would avoid premature deaths for 4,200 adults and offer annual monetized benefits ranging from $19 billion to $43 billion, and a revised PM NAAQS of 10 μg/m3 would avoid the premature death of some 1,700 adults and offer annual monetized benefits ranging $7.6 billion to $17 billion. These numbers are impressive. However, detractors claim they are difficult to replicate and open to interpretation.
For those in the CAA regulatory space, it’s well known that part of the debate around changed NAAQS standards is the cascading impacts more stringent standards have on costs associated with the need for new and different pollution control equipment, the implications of resulting changes in State Implementation Plans (SIP) because of the tighter standards, the impact on facility-specific emission unit permits, and related consequential implications.
With regard to SIP, the final revisions will trigger a process under which states and Tribes must identify to the EPA regional areas of the country that either meet the new standard or don’t. The latter areas must prepare plans that demonstrate how they will come into compliance with the new standard. This process is time-consuming and not without controversy.
Unsurprisingly, comments on the proposed rule were all over the map. Commenters questioned the scientific evidence and epidemiological data upon which the EPA relied in revising the standard, while others expressed the harm to the business community caused by the imposition of additional capital and compliance costs. Environmental justice advocates urged the agency to lower the standard for communities of color and lower income, while others pointed to World Health Organization guidelines, which reflect a recommended PM2.5 NAAQS of no more than 5.0 μg/m3. Given the strong diversity of views, the complexity of the science, and significant financial implications, it’s little wonder that changes in NAAQS standards generate Congressional interest and litigation.
Discussion
Most would agree the NAAQS program has successfully provided significant public health benefits. As with any significant new rule, the devil is in the details, and reasonable people will have differing views on the PM2.5 value to fulfill CAA standards when balancing all relevant factors. Some have expressed the view that more recent federal legislation has created valuable opportunities to improve air quality. The Infrastructure Investment and Jobs Act and the Inflation Reduction Act are viewed by many as key funding opportunities to support the development of new technologies to reduce air pollution. As noted, however, consensus on what the standard should be is elusive and will remain so. Indeed, as of this writing, it is unclear if entities intend to challenge the new PM standards in court. Some speculate litigation is inevitable.
Regardless of whether the final rule is judicially challenged, stakeholders will need to review their current operations and assess the new rule’s potential impact. This will include an assessment of whether their plant is in a nonattainment area, what their permit limits are, and how the new, more stringent standards might impact their operations. The rule is effective on May 6, 2024.
