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U.S. EPA Proposes Tighter Annual PM2.5 NAAQS and a New Secondary PM2.5 NAAQS

Posted: July 9th, 2012

Author: All4 Staff 

In 2006, the U.S. Court of Appeals for the District of Columbia declared that U.S. EPA’s primary annual fine particulate (PM2.5) National Ambient Air Quality Standard (NAAQS), currently 15 µg/m3, needed to be updated because it failed to adequately protect human health. In the years that followed, U.S. EPA prepared scientific and policy assessments in order to strengthen their knowledge on the hazards of soot pollution and to establish a NAAQS that would reduce dangerous air-borne particulates nation-wide. Scientific research has determined that exposure to fine particulate matter has been linked to serious health conditions such as cardiovascular and respiratory problems, chronic respiratory disease, and even premature death. Recently, more studies have linked health issues with low levels of PM2.5 than were previously thought.

In light of this data, U.S. EPA has proposed to tighten the annual NAAQS for PM2.5. The proposed change would lower the primary annual PM2.5 NAAQS to a range of 12-13 µg /m3 from the current standard of 15 µg /m3. The current annual PM2.5 NAAQs has been in place since 1997. A benefit and cost analysis performed by U.S. EPA estimates that the imposition of the proposed NAAQS would result in $30-$86 worth of health benefits for every dollar invested in pollution control. Additionally, U.S. EPA has proposed to ‘grandfather’ preconstruction permitting applications that are being reviewed at the time the final rule is issued. Grandfathered applications would be those draft permits and/or preliminary determinations that have been noticed for public comment prior to the finalization of the revised PM2.5 NAAQS. U.S. EPA is not proposing to change any of the New Source Review (NSR) ‘triggers’ for PM2.5 “at this time” (e.g., significance levels, significant impact levels (SILs), increments, or significant monitoring concentrations). New attainment/non-attainment designations would become effective in early 2015. The proposed changes to the annual PM2.5 standard will have no impact on the existing daily NAAQS for PM2.5 or the coarse particulate (PM10) daily standard.

Of particular interest (and concern) is the proposal of a new, distinct secondary NAAQS for PM2.5 to provide protection against visibility impairment which will be measured in terms of a visibility index using a calculated PM2.5 light extinction indicator.  The proposed secondary standard would use speciated PM2.5 mass concentrations and relative humidity data to calculate PM2.5 light extinction (similar to the Regional Haze Program), a 24-hour averaging time, a 90th percentile form (averaged over 3 years), and a visibility level set at 30 or 28 deciviews (dv).  The implications of the proposed secondary PM2.5 visibility NAAQS will be discussed in a separate blog post. 

Public comment will be accepted for 2 months immediately following the date when the proposed standards are published in the Federal Register. Public hearings have been scheduled for Philadelphia, Pennsylvania and Sacramento, California on July 17 and 19, 2012, respectively.  U.S. EPA anticipates announcing final actions by December 14, 2012.  Stayed tuned to ALL4’s blog for more details related to the PM2.5 NAAQS.


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