D.C. Circuit Court of Appeals Remands Annual Fine Particulate Matter Standards, Upholds EPA's Decision on Coarse Particles
Particulate matter is a mixture of microscopic solids and liquid droplets suspended in the air. Particulate matter is produced though all types of combustion activities and certain industrial processes. According to the Environmental Protection Agency ("EPA"), exposure to particulate matter can cause a host of serious health problems, including heart and lung diseases, decreased lung function, asthma attacks, and even premature death. Particulate matter is classified—and regulated—based on the size of the particles. Specifically, there are two types of small particulate matter: "fine" particles, or PM2.5, which have a diameter of 2.5 micrometers or less (less than one-seventh the average width of a human hair); and "coarse" particles, or PM10, which have a diameter of between 2.5 and 10 micrometers. Fine particles are believed to pose the greatest health risks, because they are small enough to lodge deeply in the lungs.
Under the Clean Air Act (the "Act"), EPA is required to establish National Ambient Air Quality Standards ("NAAQS") for pollutants considered harmful to public health and the environment. According to the Act, there are two types of national air quality standards: "primary standards," which protect public health, and "secondary standards," which protect public welfare, including protection against decreased visibility and damage to animals and vegetation, among other things.
In October 2006, EPA revised the NAAQS for PM2.5 (the "2006 PM2.5 NAAQS"). The 2006 PM2.5 NAAQS tightened the primary and secondary daily standards from 65 micrograms per cubic meter ("µg/m3") to 35 µg/m3, but retained the primary and secondary annual standards of 15 µg/m3. The 2006 PM2.5 NAAQS also retained the daily standards for PM10 of 150 µg/m3, but revoked the annual standards for PM10, based on a lack of available evidence to suggest a relationship between long-term exposure to PM10 at ambient levels and health effects. Several groups, including environmental groups and states and state agencies, among others, filed petitions for review in the D.C. Circuit Court of Appeals, challenging the 2006 PM2.5 NAAQS.
On February 24, 2009, finding that EPA failed to explain adequately why an annual level of 15 µg/m3 is requisite to protect the public health, the Court remanded the primary annual PM2.5 standard to EPA for reconsideration. The Court also remanded to EPA for reconsideration, the secondary PM2.5 standards, determining that EPA unreasonably concluded that the NAAQS are adequate to protect the public welfare from adverse effects on visibility. By contrast, the Court denied the petitions for review of the primary daily standard for PM10, as well as EPA's revocation of the primary annual standard for PM10.