U.S. Cities with Worst and Best Air Quality

The Inland Empire holds the most dubious air quality distinction in the United States. In the American Lung Association's 2026 State of the Air report, San Bernardino County ranked #1 and Riverside County #2 in the nation for ozone pollution — a position the LA metro area has held in 26 of the report's 27 years. Residents experience roughly five months of unhealthy air annually, driven by thousands of daily diesel trucks serving the region's massive warehouse and freight corridors, basin geography that traps smog inland from LA, and extreme summer heat that accelerates ozone formation. Both counties also rank in the nation's worst ten for PM2.5 particle pollution. The region is classified as an extreme ozone non-attainment zone and a severe PM2.5 non-attainment zone under federal EPA standards — the highest severity categories possible. MERV 13 is the only appropriate filter for Inland Empire households, and filters should be checked monthly and replaced every 30–45 days during summer smog season. Shop MERV 13 →

The Inland Empire holds the most dubious air quality distinction in the United States. In the American Lung Association's 2026 State of the Air report, San Bernardino County ranked #1 and Riverside County #2 in the nation for ozone pollution — a position the LA metro area has held in 26 of the report's 27 years. Residents experience roughly five months of unhealthy air annually, driven by thousands of daily diesel trucks serving the region's massive warehouse and freight corridors, basin geography that traps smog inland from LA, and extreme summer heat that accelerates ozone formation. Both counties also rank in the nation's worst ten for PM2.5 particle pollution. The region is classified as an extreme ozone non-attainment zone and a severe PM2.5 non-attainment zone under federal EPA standards — the highest severity categories possible. MERV 13 is the only appropriate filter for Inland Empire households, and filters should be checked monthly and replaced every 30–45 days during summer smog season. Shop MERV 13 →

Los Angeles has held the title of most ozone-polluted metro in the U.S. for 26 of the past 27 years per the American Lung Association. The basin's ring of mountains traps vehicle emissions and port diesel inland, driving chronic ozone and PM2.5 non-attainment. The 2025 Max AQI of 500+ reflects the January Palisades and Eaton wildfires — the most destructive in LA history — which pushed daily averages into the "Unhealthy" range for days. Year-round, a MERV 13 filter is the right baseline for LA households, with monthly checks during summer ozone season and immediate replacement during any wildfire event. Shop MERV 13 filters →

Bakersfield ranked #1 in the U.S. for annual particle pollution in the American Lung Association's 2026 State of the Air report — a position it has held for most of the past two decades. The city sits in a natural bowl at the southern end of the San Joaquin Valley, where surrounding mountains trap emissions from Kern County's massive oil and gas industry — the most productive in California — alongside agricultural dust and diesel freight. PM2.5 and ozone both exceed federal standards year-round, with summer ozone season and fall harvest dust creating the worst spikes. A MERV 13 filter replaced every 45–60 days is the only appropriate choice for Bakersfield homes. Shop MERV 13 filters →

San Diego's coastal location gives it one of the better air quality profiles among Southern California metros — earning a grade B from EPA monitoring data, with 43% of days in the "good" category in 2025. Pacific Ocean breezes continuously flush the airshed, keeping PM2.5 well below the federal standard most of the year. The primary concern is ozone, where San Diego still ranks among the top 10 worst metros nationally due to emissions drifting south from the LA basin and local vehicle traffic. Wildfire smoke from San Diego County's dry eastern canyons can push AQI into unhealthy territory during October–December Santa Ana wind events. A MERV 11 filter is the right year-round baseline, with replacement every 60–90 days. Shop MERV 11 filters →

Fresno–Madera ranked 3rd worst in the U.S. for year-round particle pollution in the American Lung Association's 2025 State of the Air report. The city faces a two-season air quality crisis: summer brings intense ozone from vehicle and agricultural emissions baking in the San Joaquin Valley heat — ozone drove 70% of monitored days in 2025 — while winter temperature inversions trap wood smoke and diesel PM2.5 from freight corridors at ground level for weeks at a time. Wildfire smoke from the Sierra Nevada adds hazardous spikes from July through October. Despite improvement over the past decade, Fresno remains one of the few U.S. cities where both ozone and particle pollution exceed federal standards year-round. A MERV 13 filter replaced every 45–60 days is the right choice for Fresno households. Shop MERV 13 filters →

Denver's Front Range holds one of the country's most stubborn ozone problems — rated "F" by the American Lung Association and classified as an extreme ozone non-attainment zone by the EPA, the highest severity level possible. Vehicle emissions and oil and gas operations — including the Suncor refinery in Commerce City — trap ozone precursors against the Rocky Mountain foothills, where summer heat drives photochemical smog. Winter brings a separate challenge: temperature inversions lock PM2.5 and wood smoke at ground level for days at a time. Wildfire smoke from Colorado's forests adds hazardous spikes each summer. A MERV 13 filter replaced every 60 days is the right choice for Front Range households year-round. Shop MERV 13 filters →

Pittsburgh ranked 12th worst in the U.S. for year-round particle pollution and 16th worst for daily PM2.5 spikes in the American Lung Association's 2025 State of the Air report — the worst record in the entire Mid-Atlantic region. Despite the steel industry's decline, the region's air quality is still shaped by natural gas production and the Shell cracker plant in Beaver County, Mon Valley coke works, diesel freight, and valley geography that traps inversions all winter. Allegheny County earned an "F" for year-round particle pollution in 2025. A MERV 13 filter replaced every 60 days is the right year-round choice for Pittsburgh households. Shop MERV 13 filters →

Detroit earned an "F" grade for both ozone and particle pollution in the ALA's 2026 State of the Air report, ranking 9th worst nationally for year-round PM2.5. The Motor City's air quality challenge is a convergence of the Southwest Detroit industrial corridor — the Marathon Oil refinery, US Steel's Zug Island, and the Ambassador Bridge freight corridor — with Great Lakes weather inversions that trap particulate matter at ground level for days. Canadian wildfire smoke increasingly spikes summer PM2.5 as well. Detroit also ranked #1 Asthma Capital in the U.S. on the 2025 Asthma Capitals report. A MERV 13 filter replaced every 45–60 days is the only appropriate choice for Metro Detroit households. Shop MERV 13 filters →

Chicago earned a grade B for overall air quality in 2025 per EPA monitoring data — a meaningful improvement from its historically poor record — though Cook County still earns an "F" for ozone from the American Lung Association. The metro's two main air quality threats are summer ozone from vehicle and industrial emissions (Lake Michigan inversions trap pollution in the urban core) and PM2.5 spikes from the industrial Southwest Side corridor and Canadian wildfire smoke drifting south each summer. The City of Chicago's Open Air monitoring network of 277 sensors shows significant neighborhood-level variation, with Pilsen and Calumet facing the heaviest industrial burden. A MERV 11 filter replaced every 60–90 days is the right year-round baseline — step up to MERV 13 during any wildfire smoke or high-ozone event. Shop MERV 11 filters →