21 August 2008

The US Environmental Protection Agency (EPA) has announced intended designations for the 24 hour PM2.5 (particulate matter below 2.5 microns) ambient air quality standard for all state lands and for Indian country.

EPA revised the national ambient air quality standard (NAAQS) for PM2.5 on September 21, 2006. The previous daily PM2.5 standard was strengthened from 65 µg/m3 to 35 µg/m3.

The EPA has sent PM2.5 designation modification letters to States, with proposed “nonattainment” designations for a number of areas. In total, the EPA identified 57 PM2.5 nonattainment areas (covering 169 whole counties and 46 partial counties) in 25 States. The EPA plans to issue final designations by December 18, 2008.

States that have areas identified as nonattainment for PM2.5 must prepare “state implementation plans” (SIP) outlining measures that are planned to bring air quality in compliance with the standards. States must meet the revised standards by 2015, with a possible extension to 2020.

Among other sources, diesel PM emissions contribute to ambient PM2.5 levels. Therefore, some of the SIP measures in the nonattainment areas will focus on reducing emissions from in-use diesel engines, such as replacement with newer, PM-controlled engines or retrofits with particulate filters.

Source: US EPA