The Clean Air Act identifies six common air pollutants that are found all over the United States and can injure health, harm the environment or cause property damage. These pollutants include:
- Carbon Monoxide
- Lead
- Nitrogen Dioxide
- Ozone
- Particulate Matter (PM10) and (PM2.5)
- Sulfur Dioxide
The United States Environmental Protection Agency (EPA) has established National Ambient Air Quality Standards (NAAQS) for each of these pollutants. If the air quality in a geographic area meets the NAAQS, it is called an attainment area; areas that do not meet the NAAQS are called nonattainment areas and must develop comprehensive state plans to reduce pollutant concentrations to a safe level.
Ambient Air Quality Standards
| Pollutant | Averaging Time | Primary / Secondary | Standard | Form |
|---|---|---|---|---|
| Ozone (O3) | 8 Hour | Primary and Secondary | 0.070 ppm | Annual fourth-highest daily maximum 8-hr concentration, averaged over three years |
| Respirable Particulate Matter (PM10) | 24 Hour | Primary and Secondary | 150 µg/m3 | Not to be exceeded more than once per year on average over three years |
| Fine Particulate Matter (PM2.5) | 24 Hour | Primary and Secondary | 35 µg/m3 | 98th percentile, averaged over three years |
| Annual | Primary | 9 µg/m3 | Annual mean, averaged over three years | |
| Secondary | 15 µg/m3 | Annual mean, averaged over three years | ||
| Carbon Monoxide (CO) | 1 Hour | Primary | 35 ppm | Not to be exceeded more than once per year |
| 8 Hour | Primary | 9 ppm | Not to be exceeded more than once per year | |
| Nitrogen Dioxide (NO2) | 1 Hour | Primary | 100 ppb | 98th percentile of 1-hour daily maximum concentrations, averaged over three years |
| Annual | Primary and Secondary | 53 ppb | Annual mean | |
| Sulfur Dioxide (SO2) | 1 Hour | Primary | 75 ppb | 99th percentile of 1-hour daily maximum concentrations, averaged over three years |
| Annual | Secondary | 10 ppb | Annual mean, averaged over three years | |
| Lead (Pb) | Rolling 3 month Average | Primary and Secondary | 0.15 µg/m3 | Not to be exceeded |
Air Quality Standard Status
In the 1990s, Davis, Salt Lake, and Utah Counties failed to attain the NAAQS for ozone, particles, carbon monoxide, and sulfur dioxide. However, Salt Lake and Davis Counties were officially re-designated to attainment status for ozone by the EPA in 1997; Salt Lake, Ogden, and Provo Cities were re-designated to attainment for carbon monoxide in 1999, 2001,and 2006 respectively.
Requests to redesignate Salt Lake County and part of Tooele County to attainment for sulfur dioxide were submitted to EPA in 2005 and the plans will be updated again in 2026 for EPA approval. Salt Lake and Utah Counties and Ogden City were redesignated to attainment for PM10 in 2020.
On September 21, 2006, the EPA issued revisions to the NAAQS for particle pollution. The EPA strengthened the 24-hour PM2.5 standard from the 1997 level of 65 µg/m3 to 35 µg/m3, and retained the current annual fine particle standard at 15 µg/m3. Salt Lake City, Provo, and Logan, UT were in PM2.5 nonattainment from 2008 until 2025. The Logan area was redesignated to attainment in 2021 and the Provo and Salt Lake areas will be redesignated to attainment in 2025.
In October 2008, the EPA strengthened the NAAQS for lead to increase protection of public health and the environment. The ambient air lead standards—both the primary (health-based) and secondary (environment-based) standards—have been revised to 0.15µg/m3 (micrograms per cubic meter of air). The previous NAAQS issued by the EPA in 1978 were ten times higher (1.5µg/m3).
In 2015, the EPA strengthened the primary and secondary ozone NAAQS from 0.075 ppm to 0.070 ppm, based on a three-year average of the annual 4th highest daily eight-hour average concentration. The standard was reviewed again in 2020, and the EPA chose to retain the standard at 0.070 ppm. In August 2018, the EPA designated portions of the Wasatch Front, Utah County, and the Uinta Basin as nonattainment areas for ozone. The Northern Wasatch Front is a moderate nonattainment area, the Southern Wasatch Front and Uinta Basin are marginal nonattainment areas.