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The Revised 24-Hour PM-2.5 Standard and Compliance Deadlines

On February 24, 2009, as a result of the suit filed against the U.S. EPA by public health and environmental groups, the U.S. Court of Appeals for the D.C. Circuit remanded the National Ambient Air Quality Standards (NAAQS) for fine particulate matter (PM2.5) to EPA for reconsideration of the annual level of the standard (which EPA left at 15 micrograms per cubic meter (µg/m3)) and reconsideration of the secondary PM2.5 NAAQS. With respect to the annual PM2.5 NAAQS, the court held that the agency “failed to explain adequately why an annual level of 15 µg/m3 is ‘requisite to protect the public health,’ including the health of vulnerable subpopulations, while providing ‘an adequate margin of safety.’ 42 U.S.C.§ 7409(b)(1).” For the secondary standards, the court held that EPA “unreasonably concluded that the NAAQS are adequate to protect the public welfare from adverse effects on visibility.” The court denied petitions for review of the primary daily standard for coarse PM and the petition for review of EPA’s revocation of the primary annual standard for coarse PM. The Court opinion can be read by clicking here.

On September 21, 2006, EPA announced with regard to primary standards for fine particles (generally referring to particles less than or equal to 2.5 micrometers (µm) in diameter, PM-2.5) that it was revising the level of the 24-hour PM-2.5 standard to 35 micrograms per cubic meter (µg/m3) and retaining the level of the annual PM-2.5 standard at 15 µg/m3. With regard to primary standards for particles generally less than or equal to 10 µm in diameter (PM-10), EPA retained the 24-hour PM-10 and revoked the annual PM-10 standard. With regard to secondary PM standards, EPA made them identical in all respects to the primary PM standards, as revised. The issue of reliability of the epidemiological time-series methodologies continues to be of concern to the Administrator. The Administrator noted in his decision that there were many sources of uncertainty and variability inherent in the inputs to the assessment and that there was a high degree of uncertainty in the resulting PM-2.5 risk estimates. Such uncertainties generally related to a lack of clear understanding of a number of important factors, including, for example, the shape of concentration-response functions, particularly when, as here, effect thresholds can neither be discerned nor determined not to exist; issues related to selection of appropriate statistical models for the analysis of the epidemiologic data; and the role of potentially confounding and modifying factors in the concentration-response relationships. For those interested in the violation areas for the revised 24-hour PM-2.5 standard, please click here.

The 24-hour PM-2.5 compliance deadlines are as follows:

10/17/06: PM NAAQS final rule published in Federal Register.
12/18/06: Effective date of the final PM NAAQS rule.
12/18/07: Based on air monitoring data collected in 2004-2006, States’ submit recommendations to EPA as to whether or not local communities are complying with the PM NAAQS.
10/8/2009: EPA makes final PM compliance designations.
11/2009: Effective date for EPA’s PM compliance designations.
11/2012: Deadline for States to submit PM State Implementation Plans (SIP).
11/2014: Attainment date.
11/2019: Attainment date with extensions.

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