On March 12, 2025, EPA Administrator Zeldin announced that the
agency, as one of its 31 historic deregulatory actions to advance
President Trump’s Day One executive orders and EPA’s
“Powering the Great American Comeback,”
will reconsider the previous administration’s rule tightening
the Particulate Matter National Ambient Air Quality Standards
(PM2.5 NAAQS). The PM2.5 NAAQS rule has raised implementation
concerns from various states across the country, including
Louisiana, and has been the subject of litigation in the U.S. Court
of Appeals for the District of Columbia Circuit (D.C. Circuit).

Final Rule Tightening PM2.5 NAAQS

On March 6, 2024, EPA issued a final rule tightening the PM2.5
NAAQS, which set the primary (health-based) annual NAAQS for PM2.5
at 9 micrograms per cubic meter (µg/m3), down from the prior
limit of 12 µg/m3. See 89 Fed. Reg. 16202 (Mar. 6, 2024). EPA also
laid out its timetable for states and the agency to implement the
tightened standards, with the first designations of areas of the
country as meeting or violating the limit targeted for 2026 and
compliance deadlines beginning in 2032. The new standards could
result in many areas of the country being designated as
nonattainment, triggering costly control requirements for
facilities located in those new nonattainment areas. The map below
depicts the counties/parishes that do not meet the annual PM2.5
NAAQS of 9 µg/m3 based on 2020-2022 air monitoring data.

In Louisiana, Caddo Parish and West Baton Rouge Parish, with
design values of 9.6 µg/m3 and 9.1 µg/m3, respectively,
would not meet the PM2.5 NAAQS of 9 µg/m3. However,
Louisiana’s Department of Environmental Quality has submitted
two “exceptional event”¹ demonstrations to the
EPA for consideration, both dealing with the Port Allen monitoring
station in West Baton Rouge Parish. The events included a Saharan
Dust that resulted in 5 days of elevated PM2.5 levels in June 2022
and a Canadian Wildfire Smoke that resulted in 2 days of PM2.5
exceedances in October 2023. Removal of these “exceptional
events” would result in West Baton Rouge Parish meeting the
PM2.5 NAAQS of 9 µg/m3.

In addition to the areas that would likely be in non-attainment,
there are also numerous areas that would be very close to exceeding
the standard, which would severely limit growth and development in
those areas. In Louisiana specifically, the following parishes have
design values that are approaching the 9 µg/m3 standard:

Litigation Challenging Final Rule Tightening PM2.5
NAAQS

OnMarch 6, 2024, a group of states, including Louisiana, and
other industry groups filed petitions for judicial review in the
D.C. Circuit, requesting the court to vacate EPA’s rule
tightening the PM2.5 NAAQS. See Commonwealth of Kentucky et al.
v. EPA et al., No. 24-1050 (D.C. Cir. Mar. 6, 2024). The
industry groups and states claimed that EPA acted in a manner
contrary to law by improperly undertaking a discretionary,
non-statutory reconsideration of the PM2.5 NAAQS, rather than a
statutorily-mandated review under CAA § 109(d) (i.e.,
five-year review), and failing to adequately consider all required
and relevant factors, including costs, in making its decision. Oral
argument was held on December 16, 2024. Most recently, on February
25, 2025, the D.C. Circuit granted EPA’s motion to hold the
case in abeyance for 60 days to allow new EPA leadership to review
the PM2.5 NAAQS.

Reconsideration of PM2.5 NAAQS

In connection with the agency’s March 12, 2025, announcement
to reconsider the PM2.5 NAAQS, EPA Administrator Zeldin noted that
the previous administration’s PM2.5 NAAQS raised serious
concerns from states and served as a major obstacle to permitting.
“Under President Trump, we will ensure air quality standards
for particulate matter are protective of human health and the
environment while we unleash the Golden Age of American
prosperity,” said Zeldin. It is important to note that any
attempt by EPA to revise the previous administration’s PM2.5
NAAQS will be subject to the formal rulemaking process, including
notice and comment periods.

In addition to a reconsideration of the PM2.5 NAAQS, EPA
announced that “it will soon release guidance to increase
flexibility on NAAQS implementation, reforms to New Source Review,
and direction on permitting obligations.”

Footnote

1 One of EPA’s 31 historic deregulatory actions
includes a reconsideration of its Exceptional Events
Rule.

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