2006 National Ambient Air Quality Standards (NAAQS) for Fine Particulate Matter (PM2.5): Designating Nonattainment Areas)

The Environmental Protection Agency (EPA) published its final revisions to the National Ambient Air Quality Standards (NAAQS) for particulate matter (particulates, or PM) on October 17, 2006. EPA’s actions leading up to and following promulgation of the 2006 standard have been the subject of considerable congressional oversight. EPA’s ongoing implementation of the standard, beginning with the designation of those geographical areas not in compliance, will likewise be an area of concern and debate among many Members of Congress, states, and other stakeholders for some time.

Promulgation of NAAQS sets in motion a process under which the states and the EPA identify areas that exceed the standard (“nonattainment areas”) using multi-year air quality monitoring data and other criteria, requiring states to take steps to reduce pollutant concentrations in order to achieve it. On November 13, 2009, EPA published its final designations for the 2006 PM NAAQS that include 120 counties and portions of counties in 18 states as nonattainment areas based on 2006 through 2008 air quality monitoring data. The final designations, which include tribal land of 22 tribes, were effective as of December 14, 2009. States have three years from the effective date to submit State Implementation Plans (SIPs), which identify specific regulations and emission control requirements that would bring an area into compliance.

In December of 2008 EPA had identified 211 counties and portions of counties (58 areas) in 25 states for designation as nonattainment for the 2006 PM NAAQS based on 2005 through 2007 data. The publication of these designations—and thus the effective date of the final designations—was delayed pending review by the current Administration. The review was initiated, in part, in response to a White House January 20, 2009, memorandum regarding regulatory review. This review and the availability of more current air quality monitoring data resulted in the final designations published in November 2009.

The 2006 NAAQS strengthened the pre-existing (1997) standard for “fine” particulate matter 2.5 micrometers or less in diameter (PM2.5) by lowering the allowable daily concentration of PM2.5 in the air. The daily standard averaged over 24-hour periods is reduced from 65 micrograms per cubic meter (μg/m3) to 35 μg/m3. However, the annual PM2.5 standard, which addresses human health effects from chronic exposures to the pollutants, is unchanged from the 1997 standard of 15 μg/m3. The 2006 NAAQS did not substantially modify the daily standard for slightly larger, but still inhalable, particles less than or equal to 10 micrometers (PM10), retaining the 24-hour standard but revoking the annual standard for PM10.

EPA’s final nonattainment designations are only for the revised 2006 24-hour PM2.5 standard. The EPA did not require new nonattainment designations for PM10. The final designations for the 2006 PM2.5 NAAQS include a few areas designated nonattainment for PM2.5 for the first time, but, as expected, the majority of the counties identified overlap with EPA’s final nonattainment designations for the 1997 PM2.5 NAAQS. EPA’s designations for the 1997 PM2.5 NAAQS included all or part of 204 counties in 20 states and the District of Columbia. Most of them were only exceeding the annual standard; only 12 counties were exceeding both the 24-hour and the annual standards. Thus, the 2006 tightening of the 24-hour standard resulted in an increased number of areas being designated nonattainment based on exceedances of both the 24-hour and the annual standards.

Date of Report: December 17, 2009
Number of Pages: 33
Order Number: R40096
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Legal Consequences of EPA's Endangerment Finding for New Motor Vehicle Greenhouse Gas Emissions

On December 15, 2009, the Environmental Protection Agency (EPA) took its most important action to date related to climate change. EPA published its final determination that the combined greenhouse gas (GHG) emissions from new, light-duty motor vehicles in the United States contribute to an “endangerment” from climate change. More precisely, EPA found that such emissions, in the words of Clean Air Act (CAA) section 202(a), “cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare.” Under section 202(a), this finding requires that EPA promulgate “standards” to control such emissions—as the agency proposed to do in advance of its endangerment determination.


Some groups have objected to the endangerment determination and the emission standards to follow, arguing they will trigger a “cascade” of unacceptable regulatory consequences under other CAA provisions. These regulatory consequences, they say, would impose unattainable GHG-concentration goals on EPA and the states, and/or economically and administratively unreasonable burdens. This report examines the CAA provisions that have figured in this debate to see whether this alleged cascade of legal consequences likely would occur.


First, the report examines CAA sections that, like section 202(a), are triggered by endangerment findings. Of these, the one most likely to require EPA regulatory action after the 202(a) endangerment finding is section 111, authorizing new source performance standards—but only as to stationary source categories emitting the largest amounts of GHGs. Section 111, however, affords EPA wide discretion in setting new source performance standards. Two other sections that arguably might be triggered are 108, requiring national ambient air quality standards, and 115, which requires states to revise their implementation plans to prevent or eliminate the endangerment of public health or welfare in a foreign country. As to these sections, however, the arguable infeasibility of the regulatory goals—even if GHG emissions in the United States are significantly reduced, atmospheric concentrations would decline little—will give EPA room to argue that regulatory action is not mandatory. Other endangerment-triggered sections of the CAA can be distinguished from section 202(a) by their explicit terms, and thus would likely not be triggered by the 202(a) endangerment finding.


Second, the report looks at CAA provisions having no endangerment trigger. Of these, EPA has conceded that two require the agency to act after it promulgates the required emission standards following the 202(a) endangerment finding. One provision would require EPA to impose “best available control technology” (BACT) on GHG emissions from any major emitting facility proposed to be constructed in a Prevention of Significant Deterioration area. The other, Title V, creates an operating permit program for stationary sources of emissions, and would require stationary sources subject to BACT under the first provision to also apply for Title V permits. As to each of these requirements, EPA has proposed a “tailoring rule” setting emission thresholds far higher than in the CAA, at least for a few years. EPA justifies the departure from statutory language under the case law doctrines of “absurd results” and “administrative necessity.”


A caveat: the issue analyzed in this report is important primarily if Congress does not enact climate change legislation that puts regulation of GHGs beyond the reach of some of the CAA provisions discussed here. In particular, the House-passed climate change bill, H.R. 2454 (the American Clean Energy and Security Act of 2009), states that three of the CAA sections treated in this report, and one CAA title, may not be used to address air pollutants based on their climate change impacts.

Date of Report: December 15, 2009
Number of Pages: 20
Order Number: R40984
Price: $29.95
Document available electronically as a pdf file or in paper form.
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