Air Quality Standards

The EPA sets National Ambient Air Quality Standards (NAAQS) to protect public health and the environment from harmful air pollutants. Under the Clean Air Act, these science-based standards define the maximum safe concentration levels for six common “criteria” pollutants found in outdoor air across the country. By establishing clear benchmarks for ground-level ozone, particulate matter, carbon monoxide, nitrogen dioxide, sulfur dioxide, and lead, the EPA ensures communities meet air quality goals that safeguard everyone—especially vulnerable populations. Understanding these standards helps explain how the government monitors air quality in your area and works to keep the air you breathe safe.

Primary and Secondary Standards

The EPA establishes two types of standards for each pollutant. Primary standards focus on protecting public health, setting limits designed to safeguard sensitive populations from harmful health effects (see Air Quality and Your Health for more details on how pollution affects you). Secondary standards address environmental protection, aiming to prevent damage to crops, forests, visibility, buildings, and wildlife. Each standard specifies an averaging time—such as hourly, daily, or annual—and a concentration level that must not be exceeded.

Monitoring and Attainment

States and local air quality agencies continuously monitor pollutant levels using certified monitoring networks. An area is considered “in attainment” if pollutant concentrations remain below the NAAQS limits over a specified period. When an area fails to meet standards and is designated “nonattainment,” state officials must develop a State Implementation Plan outlining specific control strategies, timelines, and technologies to restore compliance. This designation can affect new industrial permits, transportation projects, and other development in the region.