A nonattainment area is a geographic region where air pollution levels consistently exceed the national standards set by the Environmental Protection Agency (EPA). These designations exist under the Clean Air Act, and they trigger stricter pollution controls, additional regulatory requirements, and specific deadlines for bringing air quality back into compliance. As of recent designations, dozens of counties across the United States carry nonattainment status for at least one pollutant.
How Areas Get Designated
The EPA sets limits for six common air pollutants, known as criteria pollutants: ground-level ozone, particulate matter (both fine and coarse), carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These limits are called the National Ambient Air Quality Standards (NAAQS), and they represent the maximum concentration of each pollutant considered safe for public health, with an additional margin of safety for vulnerable groups like children, older adults, and people with respiratory conditions.
Air quality monitors stationed throughout the country continuously measure pollutant levels. When a monitor records readings above the standard over a defined period, typically averaged over one to three years depending on the pollutant, the EPA evaluates whether that area should be reclassified. State governors first recommend boundaries for the affected area, and the EPA then makes a final determination. The designated zone often covers an entire county or group of counties, even if only one monitor triggered the violation, because air pollution doesn’t stop at city limits.
What Nonattainment Means in Practice
Once an area receives a nonattainment designation, the state must develop a State Implementation Plan (SIP) outlining exactly how it will reduce pollution to meet the standard. These plans carry real consequences for local industry, transportation, and development. New factories or power plants looking to build in a nonattainment area face much tougher permitting requirements. They typically must install the most advanced pollution controls available and offset their new emissions by securing reductions from existing sources in the area, so overall pollution still drops.
Transportation projects also get affected. Federally funded highway expansions or transit projects in nonattainment areas must demonstrate they won’t worsen air quality. Regional transportation plans have to conform with the area’s pollution reduction goals, which can influence everything from highway design to public transit investment. For residents, the practical effects range from vehicle emissions testing requirements to restrictions on wood-burning stoves or fireplaces during high-pollution days.
The Most Common Pollutants Behind Designations
Ground-level ozone is by far the most frequent reason an area gets designated nonattainment. Unlike the ozone layer high in the atmosphere, ground-level ozone forms when pollutants from cars, power plants, and industrial facilities react with sunlight. This is the main ingredient in smog, and it’s particularly problematic in sunny metropolitan areas with heavy traffic. The Los Angeles basin, parts of the San Joaquin Valley in California, and portions of the Northeast corridor have struggled with ozone nonattainment for decades.
Fine particulate matter, the tiny particles small enough to penetrate deep into lung tissue and even enter the bloodstream, is the second most common trigger. These particles come from combustion sources like diesel engines, coal-fired power plants, and wildfires. In 2024, the EPA tightened the annual fine particulate standard from 12 micrograms per cubic meter to 9.0, a change expected to push additional counties into nonattainment status.
The remaining four criteria pollutants, including lead, sulfur dioxide, nitrogen dioxide, and carbon monoxide, account for far fewer nonattainment designations. Carbon monoxide nonattainment was widespread in the 1990s but has largely been resolved thanks to catalytic converters and cleaner-burning engines. Lead nonattainment areas are now rare and typically located near specific industrial sources like smelters.
Classification Levels and Deadlines
Not all nonattainment areas are treated equally. For ozone, the Clean Air Act assigns a severity classification ranging from marginal to extreme, based on how far pollution levels exceed the standard. A marginal area might have three years to reach attainment, while an extreme area like the South Coast Air Basin in Southern California can receive up to 20 years. Higher classifications come with progressively stricter requirements: lower thresholds for permitting new pollution sources, mandatory use of cleaner fuels, enhanced vehicle inspection programs, and more aggressive emission reduction targets.
For particulate matter, the classifications are more straightforward, typically moderate or serious, with corresponding deadlines of six to ten years. If an area fails to meet its deadline, the EPA can reclassify it to a higher severity level, imposing even tougher controls and potentially withholding federal highway funding.
What Happens When an Area Meets the Standard
When monitoring data shows an area has brought pollution levels below the national standard, the state can request redesignation to attainment. This isn’t automatic. The state must demonstrate it has a maintenance plan in place to keep pollution levels down for at least ten years after redesignation. The plan must include contingency measures that kick in if pollution starts creeping back up.
Many areas have successfully transitioned out of nonattainment. Pittsburgh, once notorious for industrial smog, achieved attainment for fine particulate matter. Multiple cities that violated carbon monoxide standards in the 1980s and 1990s now comfortably meet them. But some regions cycle in and out of nonattainment as standards get tightened, meaning an area can be in attainment one year and back in nonattainment the next when the EPA lowers the allowable pollution threshold.
Economic and Health Implications
Living in a nonattainment area has direct health significance. The pollutant levels that trigger these designations are associated with increased rates of asthma attacks, heart disease, premature death, and reduced lung development in children. Fine particulate matter alone is linked to tens of thousands of premature deaths annually in the United States. For individuals with existing heart or lung conditions, nonattainment-level pollution poses a measurably higher day-to-day health risk.
On the economic side, the picture is mixed. Stricter regulations raise costs for businesses that emit pollution, and permitting delays can slow new development. Some industries have relocated to attainment areas to avoid the added expense. However, the health benefits of cleaner air, measured in fewer hospital visits, fewer missed workdays, and longer lifespans, consistently outweigh compliance costs in EPA analyses. The agency estimated that the Clean Air Act’s provisions produced benefits worth over 30 times their costs between 1990 and 2020.
How to Check Your Area’s Status
The EPA maintains an interactive map called the Green Book that shows every current nonattainment area in the country, broken down by pollutant. You can search by state, county, or specific criteria pollutant to see whether your area is in attainment, nonattainment, or classified as “unclassifiable” due to insufficient monitoring data. The map also shows historical designations, so you can see whether your area previously had a nonattainment status that has since been resolved. The tool is publicly available on the EPA’s website and updated as new designations take effect.