According to the U.S. Environmental Protection Agency’s AirNow data metrics, the total number of days that were deemed “unhealthy” to “hazardous” on the Air Quality Index has declined from 2000 to 2018. Within the 35 metropolitan areas that were monitored for ozone pollution, the total number of poor air days dropped from 1562 days in 2000 to 671 days in 2018.

Overall, experts use data to show that our air quality has improved despite population and climate change.

As polluted as we think some of the major metros are, city pollution doesn’t necessarily determine a whole state’s air quality. You may be surprised to see where states rank for best to worst air quality. Here’s our full list of U.S. states in order from cleanest to poorest overall:

While you can control the air you breathe indoors with air filters, purifiers, air cleansing plants, and more, you’re not nearly as in control of the air you breathe outdoors. We compared air quality on a state level to see where people breathe easiest and where we may be inhaling dangerous particle pollutants, invisible to the human eye.

Measuring Air Quality

Luckily, the Air Quality System (AQS) compiles air pollution data collected by the U.S. Environmental Protection Agency, state, and local agencies. Along with other publicly accessible databases, we were able to rank each state for the following metrics:

• Carbon Dioxide Emissions - We compared a dataset from 2005 to 2016 and looked at the percent change in state energy-related carbon dioxide emissions by year. The state with the highest negative percentage change meant that they made progress on limiting their detrimental contributions to ozone.
• Cigarette Usage Among Adults – The CDC, or Centers for Disease Control and Prevention gathered data using sample sizes in 2017 to gain insight into the percentage of adults who smoke in each state. The higher the percentage, the lower we ranked that state.
• Air Pollution – Using America’s Health Rankings through the United Health Foundation we looked at 2019 data that looked at the average exposure to particulate matter of 2.5 microns or less. The lower the value, the less pollution, and the higher each state ranked.
• Air Quality Index – Using the Air Quality Index we gathered air quality health index rankings by cities to find which states had the most and least days categorized as low or high health risks.
• Rate of Lung Cancer Cases – The CDC also provides data on lung cancer. By averaging new lung cancer cases, rate of lung cancer deaths, and number of lung cancer deaths by state, we ranked states from lowest to highest averages. The lower the average, the less impact lung cancer had on that population, therefore the state ranked higher.

These different metrics don’t all contribute to the quality of air evenly. We re-balanced the data by placing a larger emphasis on pollution, weighting this data at 80%. Correlating metrics such as cigarette usage and lung cancer data was weighted 20%.

Want to know what states had the highest number of lung cancer cases or which states had the highest carbon dioxide emissions? Any states that tied for number of good or poor air days ended up with the same rank, which is why you’ll see repeated numbers in those columns. See where your state stood for each metric below.