High air quality is a critical component of public health. The United States Environmental Protection Agency (EPA) has established that improvements in air quality correlate with increased life expectancy. However, the World Health Organization (WHO) cautions that 99% of the global population lives in areas where air quality guidelines are not met.
To aid U.S. citizens in identifying and avoiding regions with poor air quality, Healthnews analyzed data from nearly 1,000 counties. This report presents the top 100 counties with the worst air cleanliness, ranked by air quality severity.
Healthnews analyzed air quality data from 950 U.S. counties in 2023, using information from the Environmental Protection Agency (EPA), with a focus on the number of days each county experienced poor air quality, ranging from "Unhealthy for Sensitive Groups" to "Hazardous."
These categories come from the Air Quality Index (AQI), a standardized system that uses colors to show daily air quality levels. The AQI takes into account several pollutants that the Clean Air Act regulates, including:
For more details on the AQI and how it's calculated, you can check the EPA's website section on Air Quality Index.
The counties were ranked using a scoring system with higher scores indicative of worse air quality:
Unhealthy for Sensitive Groups Days: 1 point
Unhealthy Days: 2 points
Very Unhealthy Days: 3 points
Hazardous Days: 4 points
#1 Bannock County, Idaho
Bannock County tops the list with 1 "Unhealthy for Sensitive Groups" day and 31 "Hazardous" days in 2023, primarily due to wildfire smoke. The Idaho Department of Environmental Quality notes that frequent large wildfires significantly impact air quality by contributing high levels of PM2.5 particles, posing serious health risks. The region's topography also exacerbates pollution by trapping pollutants. Bannock County has implemented "no-burn" days during high pollution periods to reduce particulate matter in the air.
#2 Riverside County, California
Riverside County recorded 46 "Unhealthy for Sensitive Groups" days, 19 "Unhealthy" days, 2 "Very Unhealthy" days, and 3 "Hazardous" days last year. Heavy traffic and industrial pollution, combined with geographical factors that trap pollutants, contribute to the poor air quality. The American Lung Association consistently ranks Riverside County among the top five worst U.S. counties for ozone pollution. The Energy Policy Institute of Chicago reports that California, primarily due to wildfire smoke, vehicle emissions, and industrial activities, has 29 of the top 30 most polluted counties.
#3 San Bernardino County, California
San Bernardino County had 48 "Unhealthy for Sensitive Groups" days, 7 "Unhealthy" days, and 1 "Very Unhealthy" day in 2023. Significant vehicular emissions, industrial activities, and frequent wildfires contribute to poor air quality, with the region often experiencing "Spare the Air" alerts advising residents to limit outdoor activities.
#4 Uintah County, Utah
Uintah County experienced 16 "Unhealthy for Sensitive Groups" days, 18 "Unhealthy" days, and 3 "Very Unhealthy" days. Oil and gas extraction activities and natural dust events are the main pollution sources. The county utilizes natural gas from local wells to power public transportation, helping reduce local air pollution levels.
#5 Maricopa County, Arizona
Maricopa County recorded 51 "Unhealthy for Sensitive Groups" days and 4 "Unhealthy" days in 2023. Vehicle emissions, construction dust, and industrial activities are major contributors to poor air quality. The region's arid climate and frequent dust storms exacerbate particulate pollution. "Dust control" teams help reduce particulate matter from construction sites and unpaved roads.
#6 Duchesne County, Utah
Duchesne County had 22 "Unhealthy for Sensitive Groups" days, 11 "Unhealthy" days, and 1 "Very Unhealthy" day. Emissions from oil and gas extraction and natural events like wildfires contribute to pollution. The county monitors and regulates emissions from local industries to counteract the pollution.
#7 Tulare County, California
Tulare County had 35 "Unhealthy for Sensitive Groups" days and 4 "Unhealthy" days last year. Agricultural activities, industrial emissions, and vehicle pollution are primary pollution sources. Tulare County is part of a regional effort to reduce agricultural emissions through sustainable farming practices.
#8 Cook County, Illinois
Cook County recorded 27 "Unhealthy for Sensitive Groups" days and 7 "Unhealthy" days. Pollution from Wisconsin and local sources like vehicle emissions and industrial activities exacerbate smog levels. The county implements green infrastructure projects to improve air quality.
#9 Inyo County, California
Inyo County experienced 12 "Unhealthy for Sensitive Groups" days, 2 "Unhealthy" days, and 5 "Hazardous" days in 2023. Dust storms and wildfires significantly impact air quality. The county studies dust storm impacts and implements measures to mitigate them.
#10 Imperial County, California
Imperial County had 11 "Unhealthy for Sensitive Groups" days, 1 "Unhealthy" day, 2 "Very Unhealthy" days, and 3 "Hazardous" days. Pollution from Mexico and local agricultural emissions are primary challenges. The county participates in cross-border air quality monitoring initiatives to address pollution from neighboring regions.
While 25 states had no counties in the top 100 list of poor air quality, the remaining 25 had varying levels of representation:
Most Affected:
Moderately Represented:
Lower Representation:
This distribution highlights the regional nature of air quality challenges, with some states facing more widespread issues than others. It's important to note that the absence of a county on this list doesn't necessarily indicate perfect air quality, but rather that it falls outside the top 100 most affected areas.
Identifying regions with significant air quality challenges is crucial for implementing effective improvement strategies. Understanding the contributing factors and local efforts can drive initiatives to enhance living conditions and public health. Since the Clean Air Act's implementation, pollution in the U.S. has decreased by 64.9%, extending the average American lifespan by 1.4 years. For information on your local air quality, check out AirNow.
