Policy Issues In the Review of the Particulate Matter NAAQS
In the ongoing review of the particulate matter National Ambient Air Quality Standards (NAAQS), there are a number of important policy issues at stake. This fact sheet outlines some of the key issues in the standard setting process that can affect the health-protectiveness of the air quality standards.
There are six main attributes of the NAAQS, each with important policy implications. Each of these aspects works in combination to determine the stringency of the standards. The attributes are:
1) Indicator Pollutant: What specific pollutant will be regulated and how it will be defined?
The only key elements of the standards that the courts rejected were the preexisting standards for PM10. The court’s reasoning was that since the PM10 standard covered all particles less than 10 microns in diameter, the PM10 and PM2.5 standards resulted in double regulation of particles less than 2.5 microns in diameter. Nevertheless, there are serious health effects associated with the PM10 size fraction, which covers particles small enough to be inhaled into the lungs.
EPA will most likely retain a standard for “fine particles” (PM2.5), and establish a new standard for “coarse particles” which will probably be defined as PM10 minus PM2.5 (PM10-2.5), particles smaller than 10 microns but larger than 2.5 microns.
The need to set a standard for a new indicator pollutant creates some difficulties for EPA. First, most of the available health research has been conducted using the prior measure, PM10. There are only a few studies that have specifically examined PM10-PM2.5. Second, a new monitoring network may need to be deployed to measure ambient concentrations of “coarse particles.” This could delay the designation of new nonattainment areas by 3-5 years.
2) Averaging Time: Over what time period will compliance with the standard be measured?
The current PM2.5 standards are measured on a 24-hour and annual average basis. The standards for PM10 were also measured on a 24-hour and annual average basis. In the case of PM2.5, the annual average standard was set to be the “controlling” standard. That is, while many areas of the country are expected to violate the annual average standard, few if any, are projected to exceed the 24-hour standard. EPA will likely retain the 24-hour and annual average averaging times during this review.
Several recent studies have pointed to effects from very short-term exposures of 1-3 hours. There are now 200 real-time monitors for PM2.5 deployed around the country, which may be used in community health studies in the future. If additional health studies point to short-term effects, EPA might consider setting a shorter-term standard in future review cycles. A shorter averaging time is not necessarily more protective of public health depending on the level and statistical form of the standard.
3) Level of the Standard: What is the actual level of the standard?
The staff typically identifies recommended ranges for the standards. For the annual average standard for PM2.5, EPA staff recommended a range between 12 - 20 µg/m3, and ultimately set the standard at the midpoint of the range, 15 µg/m3. In contrast, in its 2002 review, California set an annual average PM2.5 standard of 12 µg/m3.
In the case of the 24-hour PM2.5 standard, the EPA staff paper recommended that the standard be set within the range of 20-65 µg/m3, EPA proposed a standard of 50 µg/m3, and the final standard was set at 65 µg/m3. The level of this standard is so high that possibly only 1 area in the country (that is not also violating the annual average standard) will exceed this level.
Subsequently, EPA established a public warning level (under the Air Quality Index program) of 40 µg/m3, so the issue of a tighter 24-hour PM2.5 standard is clearly on the table. In 2002, California developed a proposal for a 24-hour PM2.5 standard of 25 µg/m3, but final consideration of this standard has been deferred pending review of some statistical issues.
Also, in its 2002 review of the state ambient air quality standards for particulate matter, California lowered its annual average PM10 standard from 30 µg/m3 to 20 µg/m3, and retained its 24-hour PM10 standard of 50 µg/m3. These levels are considerably more stringent than EPA’s PM10 standards of 50 µg/m3 annual average, and 150 µg/m3 24-hour average.
4) Statistical Form of the Standard: How many exceedances of the standards are allowed?
The 1997 24-hour PM2.5 standard was set based on a new statistical form, the “98th percentile.” Monitors will measure nonattainment with the standard if the 98th percentile of readings are above the level of the standard. Under this approach, the top two percent of the days — with the highest concentrations — are exempt from compliance determinations. In other words, there are no limits on how high pollution can rise on the seven most polluted days each year. This form of the standard defeats the purpose of the 24-hour standard, that is, to protect against high daily concentrations.
Previously, EPA standards had allowed a limited number of exceedences, averaging one per year, to be excluded from compliance determinations. The California PM standards are violated when a single exceedance of the standards occurs.
Another aspect which leads to a weaker interpretation of the standard is an EPA convention allowing “rounding down” of certain pollution concentrations close to the level of the standards.
5) Compliance Determination: How will compliance with the standards be ascertained?
The 1997 standards allowed localities to rely on “spatial averaging” of monitors to measure compliance with the standard. This approach allows high concentrations measured at a single or several monitors to be averaged with lower concentrations at other monitors to obtain an average reading for the area, perhaps, pushing the area into attainment status. In the past, nonattainment areas had been designated when a single monitor recorded violations of the standards. This latter approach is known as the “design value” method.
6) Monitoring Protocol: How will air quality be measured to determine compliance with the standards?
EPA establishes a “Federal Reference Method” that defines standards for monitoring instruments to measure ambient air quality. In addition, regulations specify how many monitors will be needed in metropolitan areas and where they should be deployed. The regulations also spell out quality assurance and reporting requirements and specify monitoring frequency.
These aspects are all important determinants of the stringency of the standards. For example, the 1997 standards relied on filter-based monitoring method, and allowed some areas to collect the filters to send to the lab for analysis only every six days. The regulations also directed EPA to site the monitors away from factories or bus depots where the highest concentrations of pollution would be expected.
In summary, opponents of clean air are very familiar with the various attributes of the air quality standards. One can expect that efforts to weaken the standards will focus not only on the obvious issue of the level of the standards, but also on the more subtle aspects of how compliance with the standard is measured.
Attachments
- NAAQS Consent Decree
- consentdecree.pdf
May 19, 1003 Consent Decree on NAAQS Review Deadlines
