The U.S. National Ambient Air Quality Standards

Air quality guidelines and standards have an important role to play in the management of air quality. Such standards are generally established and enforced by regulatory agencies in national governments. It is generally accepted that an air quality standard is a description of a level of air quality or air pollution, which is adopted by a regulatory authority as enforceable.

The US Clean Air Amendments of 1977 defined two kinds of air quality standards: primary standards set limits to protect public health, including the health of “sensitive” populations such as asthmatics, children, and the elderly; secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings. The amendments also define air quality levels that cannot be exceeded in specified geographic areas for “prevention of significant deterioration” (PSD) of the air of those areas. Although they are called “increments” over “baseline air quality” in the law, they are in effect tertiary standards, which are set at lower ambient levels than either the primary or secondary standards. The PSD program applies to any “major emitting facility” in attainment areas. For 28 named categories a major emitting facility is one with a “potential to emit” 100 tons or more per year of any regulated. However, any source is regulated under PSD if it has a potential to emit 250 or more tons per year.

Table1. US Federal Primary and Secondary Ambient Air Quality Standards (NAAQS).¹

Table1 is some of the US Federal primary and secondary ambient air quality standards. Besides, standards related to ozone and sulfur oxides have also be set. To attain this standard, the 3-year average of the fourth-highest daily maximum 8-h average ozone concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm. And for sulfur oxides, the 3-year average of the weighted annual mean PM_2.5 concentrations from single or multiple community-oriented monitors must not exceed 15.0 μg m^?3.

Table 2. US Federal Prevention of Significant Deterioration (PSD) Increments¹

Increments are said to be "consumed" as new sources are given permits that allow pollution to be introduced into these areas. Jurisdictions with authority to issue permits may choose to “allocate” portions of a PSD increment (or of the difference between actual air quality and the primary or secondary standard) for future consumption, rather than to allow its consumption on a first-come, first-served basis.

The states are required to submit to the federal EPA plans, known as State Implementation Plans (SIP), showing how they will achieve the standards in their jurisdictions within a specified time period. If after that time period there are areas within the states where these standards have not been attained, the states are required to submit and obtain EPA approval of revised plans to achieve the standards in these “nonattainment” areas. EPA also designates certain areas where the standards are being met, but which have the potential for future nonattainment, as Air Quality Maintenance Areas (AQMA). Such regions have stricter requirements than attainment areas for the granting of permits for new sources of the pollutant not in attainment status.

To sum up, the U.S. national environmental air quality standards consist of four parts: pollutant program, average time, concentration limit, and compliance statistical requirements. In the 40 years since 1971, the U.S. environmental protection agency has revised the environmental air quality standard as many as 11 times, and revised the environmental air quality standard for all pollutants.

In the process of making and revising the national environmental air quality standard, the pollutant project in the standard was adjusted to 7 kinds from 6 kinds of SO₂, TSP, photochemical oxidant, HC, NO₂, CO, etc., which abolished TSP and HC, and increased PM₁₀, PM_2.5 and Pb.

In the process of making and revising the national environmental air quality standard, the statistical requirements for reaching the standard are constantly adjusted, and the earliest regulation on the number of exceeding the standard is gradually canceled, while scientific statistical indicators such as percentile and annual high value are adopted.

References

• Vallero, D. A. (2008). 24 - air quality criteria and standards. Fundamentals of Air Pollution, 659-678.

• Vallero, D. (2014). Chapter 3 - the science of air pollution. Fundamentals of Air Pollution, 43-81.

• Esworthy, R. (2013). The national ambient air quality standards (naaqs) for particulate matter (pm): epa's 2006 revisions and associated issues.

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