National Ambient Air Quality Standards for Particulate Matter

Based on its review of the air quality criteria and national ambient air quality standards (NAAQS) for particulate matter (PM), EPA proposes to make revisions to the primary and secondary NAAQS for PM to provide requisite protection of public health and welfare, respectively, and to make corresponding revisions in monitoring reference methods and data handling conventions for PM. With regard to primary standards for fine particles (particles generally less than or equal to 2.5 micrometers ([mu]m) in diameter, PM<INF>2.5</INF>), EPA proposes to revise the level of the 24-hour PM<INF>2.5</INF> standard to 35 micrograms per cubic meter ([mu]g/ m<SUP>3</SUP>), providing increased protection against health effects associated with short-term exposure (including premature mortality and increased hospital admissions and emergency room visits) and to retain the level of the annual PM<INF>2.5</INF> standard at 15 [mu]g/ m<SUP>3</SUP>, continuing protection against health effects associated with long-term exposure (including premature mortality and development of chronic respiratory disease). The EPA solicits comment on alternative levels of the 24-hour PM<INF>2.5</INF> standard (down to 25 [mu]g/m<SUP>3</SUP> and up to 65 [mu]g/m<SUP>3</SUP>) and the annual PM<INF>2.5</INF> standard (down to 12 [mu]g/m<SUP>3</SUP>), and on alternative approaches for selecting the standard levels. With regard to primary standards for particles generally less than or equal to 10 [mu]m in diameter (PM<INF>10</INF>), EPA proposes to revise the 24-hour PM<INF>10</INF> standard in part by establishing a new indicator for thoracic coarse particles (particles generally between 2.5 and 10 [mu]m in diameter, PM<INF>10-2.5</INF>), qualified so as to include any ambient mix of PM<INF>10-2.5</INF> that is dominated by resuspended dust from high-density traffic on paved roads and PM generated by industrial sources and construction sources, and excludes any ambient mix of PM<INF>10-2.5</INF> that is dominated by rural windblown dust and soils and PM generated by agricultural and mining sources. The EPA proposes to set the new PM<INF>10-2.5</INF> standard at a level of 70 [mu]g/m<SUP>3</SUP>, continuing to provide a generally equivalent level of protection against health effects associated with short-term exposure (including hospital admissions for cardiopulmonary diseases, increased respiratory symptoms and possibly premature mortality). Also, EPA proposes to revoke, upon finalization of a primary 24-hour standard for PM<INF>10-2.5</INF>, the current 24- hour PM<INF>10</INF> standard in all areas of the country except in areas where there is at least one monitor located in an urbanized area (as defined by the U.S. Bureau of the Census) with a minimum population of 100,000 that violates the current 24-hour PM<INF>10</INF> standard based on the most recent three years of data. In addition, EPA proposes to revoke the current annual PM<INF>10</INF> standard upon promulgation of this rule. The EPA solicits comment on alternative approaches for selecting the level of a 24-hour PM<INF>10-2.5</INF> standard, on alternative approaches based on retaining the current 24-hour PM<INF>10</INF> standard, and on revoking and not replacing the 24-hour PM<INF>10</INF> standard. With regard to secondary PM standards, EPA proposes to revise the current standards by making them identical to the suite of proposed primary standards for fine and coarse particles, providing protection against PM-related public welfare effects including visibility impairment, effects on vegetation and ecosystems, and materials damage and soiling. Also, EPA solicits comment on adding a new sub-daily PM<INF>2.5</INF> standard to address visibility impairment.