U.S. air quality trends

What causes bad air quality?

According to the World Health Organization, air pollution is environmental contamination “by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere.”

Geography (e.g., pollutants can become trapped in high-elevation areas or pushed from coastal areas) and weather conditions (e.g., dust storms) can affect the quality of the air, but “most pollutants come from human activity,” according to the University Corporation of Atmosphere Research Center for Science Education.

The WHO cites household combustion devices, motor vehicles and industrial facilities as some of the largest contributors to the following air pollutants:

• Particulate matter
• Carbon monoxide
• Ozone
• Nitrogen dioxide
• Sulfur dioxide

These pollutants also contribute to greenhouse gas emissions, so it’s crucial we continue to tackle the issue of air pollution — for both our health and the health of the planet.

Metros with the best air quality

To find the metro areas with the best air quality nationally, we looked at which areas had the lowest bad air scores (see our methodology for more details on our scoring system).

Based on national air quality index (AQI) data, we found that the five metros with the best air quality in 2022 are as follows:

1. Longview, Washington
2. Urban Honolulu, Hawaii
3. Coeur d'Alene, Idaho
4. Kahului-Wailuku-Lahaina, Hawaii
5. Bellingham, Washington

All five of these metro areas are in the Western U.S. Washington also showed up as No. 2 — and Idaho as No. 7 — in our recent rankings for the greenest states.

» SEE “GREEN” RANKINGS: Greenest states in the U.S.

According to the Environmental Protection Agency, “salty air from the ocean’s surface can help to reduce ozone air pollution, particularly in coastal areas” — this could have something to do with Hawaii’s double appearance here.

1. Longview, Washington

The Longview metropolitan area includes Cowlitz County in the southwestern part of the state. Our analysis shows that 99.52% of all days with a registered AQI value in 2022 in the Longview metro were good air days, with an AQI value of 50 or below. There were 209 total good air days and just one “moderate” (AQI value from 51 to 100) air quality day. Its bad air score was just 0.005.

Longview’s median AQI value during the research period was 13 (the second-lowest registered), and its maximum AQI value was 54 (tied for best among cities that qualified). According to Census Reporter, which compiles data from the U.S. Census Bureau’s American Community Survey, the Longview metro area covers 1,141 square miles and had a population of 111,524 in 2021, making for 97.7 people per square mile.

2. Urban Honolulu, Hawaii

The Urban Honolulu metro includes more than a million people spread over just 600.6 square miles and encompasses the entire island of Oahu. AQI data for 2022 shows that the metro saw 181 good air days out of 182 — the remaining day was classified as “unhealthy for sensitive groups” (AQI value of 101 to 150). Its bad air score was 0.008.

Urban Honolulu had the highest maximum AQI value of any area in our top five (142), but its median AQI value was only 29.

Census data via Census Reporter shows that in 2021 the Urban Honolulu metro had a high rate — more than 1.5 times the national average — of carpoolers (14% vs. 8%).

3. Coeur d’Alene, Idaho

The Coeur d’Alene metro area in northern Idaho is home to Lake Coeur d’Alene, the Coeur d’Alene Mountains and the Kootenai County seat of Coeur d’Alene (what 19th-century French traders called the Schitsu'umsh people, meaning “heart of the awl”).

The Coeur d’Alene metro registered 179 good air days and two moderate days out of 181 reported in 2022. Its maximum AQI value during the reporting period was 57, and its median AQI value was 10 — the lowest of any metro area that qualified. Coeur d’Alene’s bad air score was tied with Kahului-Wailuku-Lahaina’s at 0.011, but we gave it the edge because of its lower maximum and median AQI values for the year.

According to census data, the metro’s population in 2021 was 179,789, spread over 1,237.8 square miles, making for 145.3 people per square mile.

4. Kahului-Wailuku-Lahaina, Hawaii

AQI data from 2022 shows that the Kahului-Wailuku-Lahaina, Hawaii, metro area registered 179 good air days out of 181 total, with two moderate days logged. Its maximum AQI value was 72, and its median was 18. Its bad air score was 0.011.

It’s possible people are spending less time in their cars than average in this metro area; according to census data, the average commute time in Kahului-Wailuku-Lahaina was 22 minutes in 2021, slightly under both the state (25.3 minutes) and national (25.6 minutes) averages.

As of 2021, the Kahului-Wailuku-Lahaina metro spanned 1,161.5 square miles and had a population of 164,268 — or 141.4 people per square mile.

5. Bellingham, Washington

In the Bellingham metropolitan area, there were 182 days with reported AQI values in 2022. Out of these, 179 were classified as good air days, while three were categorized as moderate air days. The resulting 98.35% good air day rate was fifth among qualifying areas in 2022. Its bad air score was 0.016.

According to 2021 census data, the Bellingham metro area, located in northwest Washington, had a population of 228,831. The area covers approximately 2,107.9 square miles and has a population density of 108.6 people per square mile.

Which metros have the worst air quality?

Interestingly, according to reported AQI data in 2022, four of the top five metro areas with the highest bad air scores are in California. Texas’ Houston-The Woodlands-Sugar Land metro makes a showing at No. 4.

1. Riverside-San Bernardino-Ontario, California
2. Los Angeles-Long Beach-Anaheim, California
3. Hanford-Corcoran, California
4. Houston-The Woodlands-Sugar Land, Texas
5. El Centro, California

While California ranks poorly for air quality due to climate conditions, the state’s green initiatives make it a standout in terms of recycling, composting and renewable energy use — it was the No. 6 greenest state in our recent study.

This might not come as a surprise; these California metros are all surrounded by — if not right in the middle of — areas at high risk of wildfire, according to KQED in Northern California.

Still, California ranked No. 6 in our study on the greenest states in the U.S. — while the state faces hazardous conditions due to climate change and the danger of wildfires, its residents recycle and compost a significant part of its waste (41.8% and 11.5%, respectively), and 41.1% of its power generation comes from renewable sources of energy.

What's going on in Houston?

Heidi Bethel of the EPA named the pollutants around Houston in a report titled “A Closer Look at Air Pollution in Houston: Identifying Priority Health Risks.” Bethel cited “tailpipe emissions from cars, trucks and buses; toxic pollutants emitted into the air by more than 400 chemical manufacturing facilities, including 2 of the 4 largest refineries in the U.S.; [and] the petrochemical complex along the Houston Ship Channel and the Port of Houston.”

The report also mentions “many small operations spread geographically across Greater Houston, such as surface coating processes, dry cleaners, gas stations, printing processes, restaurants, charcoal barbecues, and gasoline-fueled lawn maintenance equipment.”

Source: Based on 2022 EPA data

Metros with the most air quality improvement over 10 years

When we compared 2012 air quality data with figures from 2022, we found that four of the top five metros with the most improved air quality are in the Eastern U.S. — in Georgia, Indiana and the Washington, D.C., area. Missoula, Montana, was the outlier (No. 4).

1. Rome, Georgia
2. Lafayette-West Lafayette, Indiana
3. Fort Wayne, Indiana
4. Missoula, Montana
5. Washington, D.C.-Arlington-Alexandria

1. Rome, Georgia

The Rome metropolitan area covers about 510 square miles and includes the Appalachian Mountain foothills northwest of Atlanta. Between 2012 and 2022, its bad air score decreased by about 89%, from 0.866 to 0.097. Among the 25 most-improved metros, it had the third-highest percentage of good air days in 2022 (90.25%).  As of 2021, the Rome metro area had a population of 98,771.

2. Lafayette-West Lafayette, Indiana

The Lafayette-West Lafayette metro area’s bad air score decreased from 0.668 to 0.132 (about 80%) between 2012 and 2022. The metro area contains a population of 224,253, many of whom live in Lafayette, the county seat of Tippecanoe County, and in West Lafayette, home to Purdue University. Its percentage of good air days in 2022 (86.81%) was fifth among the 25 most improved.

3. Fort Wayne, Indiana

Indiana shows again in the top five for most-improved air quality with the Fort Wayne metro area, which is situated near the northeastern corner of the state. In 2012, its bad air score was 0.684, and it had a good air day percentage of 33.88%. In 2022, its bad air score was 0.203, a 70% drop.

4. Missoula, Montana

If you’re an outdoorsy person, you might have dreamed of trout fishing near Missoula, which is between Glacier National Park and Yellowstone National Park. The Missoula metro area sits in the western part of the state, not far from the border with Idaho. Its 2012 bad air score was 0.814 (the sixth-worst among the list of 25 most-improved metros), but by 2022, the score dropped to 0.342, or about 58%.

5. Washington, D.C.-Arlington-Alexandria, Virginia

The Washington, D.C.-Arlington-Alexandria metro, which includes the capital, saw a 57% improvement in its bad air score from 2012 to 2022. In 2012, its bad air score was 0.788, with only 27.60% of days with a registered AQI value categorized as good air days. In 2022, these figures improved to 0.336 and 67.15%, respectively.

Bottom line

According to the WHO, 99% of the global population breathes air that “exceeds WHO guideline limits and contains high levels of pollutants, with low- and middle-income countries suffering from the highest exposures.” The good news, though, is that the U.S. as a whole saw 12.83% more good air days in 2022 than it did in 2012.

Jamie Mitri, an environmental engineer and the founder of Moss Pure, a company that uses live moss to filter air, said about the improvement in national air quality: “There's a lot more acknowledgment and interest in air quality, especially since COVID. Air quality is now on everyone's mind and I don't think this is just a trend — it's the future.”

All the experts we spoke with seemed to agree that small steps are significant — this could be adopting wind or solar power, driving an electric or hybrid vehicle or composting/recycling when you can.

Rick Sun, an indoor air quality expert, said about these air quality trends: “As the air quality trends shift, so do the solutions for addressing air pollution. There’s a growing movement toward emissions reduction, clean energy and sustainable transport. Governments, businesses and individuals can take steps to reduce their impact on pollution and create a better future.”

» MORE: Where your solar savings go the furthest

Methodology

The ConsumerAffairs Research Team looked at air quality index (AQI) data for metropolitan statistical areas from the Environmental Agency (EPA) for 2012 and 2022 and developed a formula for a “bad air score” for each year. The bad air score for each year is calculated by multiplying the number of days with a registered AQI value falling in each AQI range by the following multipliers:

• Moderate (x1)
• Unhealthy for sensitive groups (x1.5)
• Unhealthy (x2)
• Very unhealthy (x2.5)
• Hazardous (x3)

The sum is then divided by the total number of days in the year with a registered AQI value to get the bad air score. The higher the bad air score is, the worse the air quality is. Only metro areas with a minimum of 180 days of reported AQI data in a year were included in the analysis.

Example: bad air score for El Centro in 2022

• 122 moderate air days(1) + 23 unhealthy for sensitive groups days(1.5) + 4 unhealthy days(2) + 2 very healthy days(2.5) + 5 hazardous days(3) = 184.5
• 184.5/238 days with registered AQI in 2022 = 0.775 bad air score

References

ConsumerAffairs writers primarily rely on government data, industry experts and original research from other reputable publications to inform their work. Specific sources for this article include:

1. Environmental Protection Agency, “Air Data: Air Quality Data Collected at Outdoor Monitors Across the US.” Accessed June 9, 2023.Link Here
2. U.S. Census Bureau, “Explore Census Data.” Accessed June 9, 2023.Link Here
3. AirNow, “Air Quality Index (AQI) Basics.” Accessed June 20, 2023.Link Here
4. World Health Organization, “Air pollution.” Accessed June 9, 2023.Link Here
5. Census Reporter, “Census Reporter.” Accessed June 9, 2023.Link Here
6. UCAR, “What is Air Quality?” Accessed June 9, 2023.Link Here
7. Environmental Protection Agency, “Modeling Research Shows How Salty Ocean Air Impacts Ozone Pollution.” Accessed June 9, 2023.Link Here
8. KQED, “MAP: Do You Live in a High-Risk Fire Zone?” Accessed June 9, 2023.Link Here