Cities with the Biggest Declines in Air Pollution

While the recent wildfires in Western states have introduced new concerns about air quality, the United States has made huge strides in the reduction of air pollution in recent decades. As a result of the Clean Air Act and modern pollution control technologies, emissions of common air pollutants have dropped by more than 70 percent since 1970, according to new data from the Environmental Protection Agency (EPA).2 These reductions, which the EPA claims have significantly improved the environment and human health, occurred despite a growing population, increased energy use, and more cars on American roads.

The EPA measures air quality through the Air Quality Index, or AQI. The AQI rates air quality with values between 0 and 500; an AQI over 100 is considered unhealthy for sensitive groups, and anything over 150 is unhealthy for everyone. Major pollutants accounted for by the AQI and regulated by the Clean Air Act include ground-level ozone, particle pollution (or particulate matter), carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.

Cities with the Biggest Declines in Air Pollution - Infographics showing the U.S. coastal states with significant emissions reductions, with states shaded based on the change in emissions.

States that have witnessed the sharpest declines in air pollutant emissions (excluding wildfires) within the last decade are largely concentrated in the South, Northeast, Great Lakes, and West Coast. Ohio witnessed a 48.5 percent reduction in emissions from 2009 to 2019. This was closely followed by other states in the Great Lakes region, including Indiana, Michigan, Pennsylvania, and Wisconsin, whose emissions dropped between 47.9 and 42.1 percent. Coastal states in particular stand out among those with declines, with emissions in nearly every state on the East Coast and West Coast dropping between approximately 20 and 45 percent.

A strong reduction in emissions hasn’t entirely reduced air pollution levels in certain states. Even though California, for example, has reduced emissions by 41.1 percent, the state continues to struggle in combating smog. California’s car culture, topography, year-round mild climate, and wildfires pose a challenge to the state’s clean air standards. While 47 states reduced their emissions, Missouri, Alaska, and North Dakota actually increased emissions during the same time period.

TRENDING
If you live in an area that regularly deals with poor air quality, it’s important to replace your home air filters often. For especially bad areas and/or if you suffer from a respiratory illness, consider purchasing MERV 13 air filters, which provide extra protection.

To determine the metropolitan areas with the largest decreases in air pollution over the past decade, researchers at Filterbuy ranked locations by the percentage change in median AQI between the five-year period ending in 2019 and the five-year period ending in 2009. Five-year periods were used to lessen the effects of annual variability in AQI on the overall results. To improve relevance, metropolitan areas were grouped into cohorts based on population size: large (1,000,000 or more), midsize (350,000-999,999), and small (less than 350,000).

Here are the metropolitan areas with the biggest improvement in air quality over the past decade.