National Ambient Air Quality Standards

National ambient air quality standards (NAAQS) are defined in the Clean Air Act as amounts of pollutant above which detrimental effects to public health or welfare may result. NAAQS have been established for the following criteria pollutants:

• particulate matter
  • PM10 is particulate matter less than 10 microns in diameter
  • PM2.5 is less than 2.5 microns in diameter
  • total suspended particulate matter is called PM or sometimes TSP
• sulfur dioxide (SO2),
• nitrogen dioxide (NO2),
• ozone,
• carbon monoxide (CO) and
• lead (Pb).

Primary NAAQS are set at levels to protect human health; secondary NAAQS are to protect human welfare effects including visibility as well as plant and materials damage.

An area that is found to be in violation of a primary NAAQS is labeled a nonattainment area; an area once in nonattainment but recently meeting NAAQS, and with appropriate planning documents approved by EPA, is a maintenance area; all other areas are attainment or unclassified (due to lack of monitoring). State air quality agencies can provide up-to-date locations of local nonattainment areas (PM2.5 is a newly regulated pollutant, so attainment/ nonattainment status had not been determined at the time of publication of this document; monitoring must take place for at least 3 years before designation can be made, which means PM2.5 status will likely not be known until at least 2003). States are required through their SIPs to define programs for implementation, maintenance, and enforcement of the NAAQS within their boundaries. Wildland fire in and near nonattainment areas will be scrutinized to a greater degree than in attainment areas and may be subject to general conformity rules. Extra planning, documentation, and careful scheduling of prescribed fires will likely be required to minimize smoke effects in the nonattainment area to the greatest extent possible. In some cases, the use of fire may not be possible if significant impacts to a nonattainment area are likely.

The major pollutant of concern in smoke from fire is fine particulate matter, both PM10 and PM2.5. Studies indicate that 90 percent of all smoke particles emitted during wildland burning are PM10, and 90 percent of PM10 is PM2.5 (Ward and Hardy 1991). The most recent human health studies on the effects of particulate matter indicate that fine particles, especially PM2.5, are largely responsible for health effects including mortality, exacerbation of chronic disease, and increased hospital admissions (Dockery and others 1993; Schwartz and others 1996).

Natural Events Policy

PM10 NAAQS exceedances caused by natural events are not counted toward nonattainment designation if a State can document that the exceedance was truly caused by a natural event and prepares a natural events action plan (NEAP) to address human health concerns during future events (Nichols 1996). Natural events are defined by this policy as wildfire, volcanic, seismic, and high wind events.

A wildfire NEAP should include commitments by the State and stakeholders to:

• Establish public notification and education programs.
• Minimize public exposure to high concentrations of PM10 due to future natural events such as by:
  • Identifying the people most at risk.
  • Notifying the at-risk public that an event is active or imminent.
  • Recommending actions to be taken by the public to minimize their pollutant exposure.
  • Suggesting precautions to take if exposure cannot be avoided.
• Abate or minimize controllable sources of PM10 including the following:
  • Prohibition of other burning during pollution episodes caused by wildfire.
  • Proactive efforts to minimize fuel loadings in areas vulnerable to fire.
  • Planning for prevention of NAAQS exceedances in fire management plans.
• Identify, study, and implement practical mitigating measures as necessary.
• Periodic reevaluation of the NEAP.

Ozone and Fire

Ozone is a criteria air pollutant, but there is little monitoring or research data that directly link fire emissions with ground-level ozone concentrations. Regulating efforts to reduce ozone have therefore focused on more obvious industrial and urban sources of the pollutants that form ozone (NOX and VOCs). Fires are known to emit VOCs and a minor amount of NOX, but much is uncertain about the magnitude of ozone formation in the plume, the degree of mixing with urban sources of ozone precursors, and transport of ozone to ground level. EPA plans to begin including fire emissions in future regional ozone strategy modeling. Field observations of ozone formation in smoke plumes from fires date back nearly 25 years when measurements from aircraft detected ozone at the edge of forest fire smoke plumes aloft. A recent study (Wotawa and Trainer 2000) did link high ground-level ozone concentrations to forest fire plumes that had been transported great distances. Atmospheric and Plume Chemistry explores these issues more fully.