Exercising one of its most important and far-reaching powers under the Clean Air Act, the Environmental Protection Agency (EPA) has lowered the primary annual National Ambient Air Quality Standard (NAAQS) for fine particulate matter (PM2.5) from 12 micrograms per cubic meter (ug/m3) down to 9 ug/m3, changing the game on air quality permitting for much of the U.S. EPA’s February 7, 2024 final rule, which will become effective 60 days following its publication in the Federal Register, represents a reversal of the Trump administration’s decision to retain the PM2.5 standard of 12 ug/m3 set under the Obama administration in 2012. The lower standard will set off a chain reaction of additional requirements for state air agencies, and ultimately industrial sources, in places designated as nonattainment with the new standard, but one impact of the new standard will be felt almost immediately: increased difficulty in obtaining air permits.

The most obvious impact of a new, lower NAAQS is the possibility of new nonattainment areas, which could result in new emission control requirements for some sources. However, this impact will not be felt for several years, since implementation of new control strategies in nonattainment areas could take seven years or more. EPA even claims 99% of the U.S. will attain the standard by 2032 without any additional controls due to significant improvements in air quality already underway and new rules EPA has already proposed or adopted. If true, the impact of new nonattainment plans imposing additional emission control requirements may be minimal.

The requirement for states to develop new “infrastructure” plans to implement the new standard will also take many years to implement. Infrastructure requirements are typically as mundane as they sound, but include the requirement for states to demonstrate that they do not significantly contribute to downwind air quality problems. That requirement is notable because it is the basis for EPA’s controversial “good neighbor” rules, which have forced wide-ranging additional emission control requirements in cases where EPA has determined that state efforts to curb emissions were not sufficient to protect downwind states. EPA’s good neighbor rules have also spawned significant litigation, including a recent argument at the Supreme Court. Nonetheless, like nonattainment plans, any new “good neighbor” control requirements arising out of new infrastructure plans are still many years away.

Far more immediate than any requirements associated with new nonattainment or infrastructure plans are impacts on air permitting, including for sources that have already submitted applications and are awaiting permit issuance. Under the Clean Air Act, all applications for construction permits must be supported by a demonstration that the project under review will not cause or contribute to a violation of the NAAQS. For major source and major modification permits, that demonstration is typically made via dispersion modeling. However, modeling will no longer be an option for making the necessary demonstration for sources located in areas that are already above the new lower standard of 9 ug/m3 because a model will never predict that increased emissions will result in lower ambient concentrations. Even in areas that are below the new 9 ug/m3 standard, the required demonstration will be far more difficult to make because there will be less margin available for additional emissions. Additionally, once nonattainment designations are made, new nonattainment permitting requirements will kick in, including the requirement to obtain emissions offsets and to install controls to meet the more stringent “lowest achievable emission rate” standard, long before nonattainment plans require new controls directly.

A final effect of the lower standard that may be felt across the U.S. is the potential for more air pollution warnings; i.e., more “yellow” and “orange” days, based on EPA’s color-coded “Air Quality Index.” More frequent alerts are sure to occur once that index reflects the new standard. Ironically, the increased frequency of warnings could lead the general public to believe that air quality is degrading, when in fact the opposite is true, according to EPA’s own analysis.