Understanding Grades and Tables

  1. Home
  2. Research & Reports
  3. State of the Air
  4. About this Report
  5. Understanding Grades and Tables

Understanding Grades and Counties

See Methodology for a full explanation of data sources and calculations made for state grades. 

Notes for state grades tables:

  1. Not all counties have monitors for either ozone or particle pollution. If a county does not have any monitoring data for either pollutant, that county’s name is not on the list in these tables. The decision about siting monitors in a county is made by the state and the U.S. Environmental Protection Agency, not by the American Lung Association.
  2. INC (Incomplete) indicates that monitoring data is available for at least one year in that county, but not all three years.
  3. DNC (Data Not Collected) indicates that data on that particular pollutant was not collected in that county during the three years covered in the report.
  4. The Weighted Average (Wgt. Avg.) was derived by adding the three years of individual level data (2020-2022), multiplying the sums of each level by the assigned standard weights (i.e., 1=orange, 1.5=red, 2.0=purple and 2.5=maroon) and calculating the average. Grades are assigned based on the weighted averages as follows: A=0.0, B=0.3-0.9, C=1.0-2.0, D=2.1-3.2, F=3.3+.
  5. The Design Value is the calculated concentration of a pollutant based on the annual National Ambient Air Quality Standard for PM2.5, which is 9 µg/m3. Counties with design values of 9.0 or lower received a grade of “Pass” for Annual PM2.5. Counties with design values of 9.1 or higher received a grade of “Fail.”

Notes for at-risk groups tables:

  1. Adding across rows does not produce valid estimates. Adding the at-risk categories (asthma, COPD, poverty, etc.) will double-count people who fall into more than one category.
  2. Total Population is based on 2022 U.S. Census and represents the at-risk populations in counties with ozone or PM2.5 pollution monitors; it does not represent the entire state’s sensitive populations.
  3. Those 18 & under and 65 & over are vulnerable to ozone and PM2.5. Do not use them as population denominators for disease estimates—that will lead to incorrect estimates.
  4. Pediatric asthma estimates are for those under 18 years of age and represent the estimated number of people in that age group who had asthma in 2022 based on the state rates, when available, or national rates when not (Behavioral Risk Factor Surveillance System, or BRFSS), applied to county population estimates (U.S. Census).
  5. Adult asthma estimates are for those 18 years of age and older and represent the estimated number of people in that age group who had asthma during 2022 based on state rates (BRFSS) applied to county population estimates (U.S. Census).
  6. COPD estimates are for adults 18 and over who had ever been diagnosed with chronic obstructive pulmonary disease, which includes chronic bronchitis and emphysema, based on state rates (BRFSS) applied to county population estimates (U.S. Census).
  7. Lung cancer estimates are for all ages and represent the estimated number of people newly diagnosed with lung cancer in 2020 based on state rates (StateCancerProfiles.gov) applied to county population estimates (U.S. Census).
  8. Cardiovascular (CV) disease estimates are for adults 18 and over who have been diagnosed within their lifetime, based on state rates (BRFSS) applied to county population estimates (U.S. Census). CV disease includes coronary heart disease, stroke and heart attack.
  9. Pregnancy estimates are for females 18-49 and based on state rates of pregnancies resulting in live births applied to population estimates (U.S. Census).
  10. Poverty estimates include all ages and come from the U.S. Census Bureau’s Small Area Income and Poverty Estimates program. The estimates are derived from a model using estimates of income or poverty from the Annual Social and Economic Supplement and the Current Population Survey, 2021. Puerto Rico poverty estimates come from the U.S. Census Bureau’s American Community Survey, 2018-2022.
  11. People of color are defined as anyone Hispanic or as non-Hispanic Black, Asian, American Indian/Alaska Native, Native Hawaiian and Other Pacific Islander, or two or more races, based on 2022 county population estimates (U.S Census). Puerto Rico race and ethnicity estimates come from the U.S. Census Bureau’s American Community Survey, 2018-2022.
  12. Based on a request from Connecticut, the Census Bureau shifted from providing population estimates by county to county-equivalent Planning Regions for the state starting with 2022 data. As air quality data continues to be county-based and Planning Regions are incompatible with historic Connecticut counties, Census Bureau population estimates from 2021 are used in this year’s report. Disease rates are still from the latest year available.

Did You Know?

  1. Nearly four in ten people in the U.S. live where the air they breathe earned an F in “State of the Air” 2024.
  2. More than 131 million people live in counties that received an F for either ozone or particle pollution in “State of the Air” 2024.
  3. Nearly 44 million people live in counties that got an F for all three air pollution measures in “State of the Air” 2024.
  4. Breathing ozone irritates the lungs, resulting in inflammation—as if your lungs had a bad sunburn.
  5. Breathing in particle pollution can increase the risk of lung cancer.
  6. Particle pollution can cause early death and heart attacks, strokes and emergency room visits.
  7. Particles in air pollution can be smaller than 1/30th the diameter of a human hair. When you inhale them, they are small enough to get past the body's natural defenses.
  8. Ozone and particle pollution are both linked to increased risk of premature birth and lower birth weight in newborns.
  9. If you live or work near a busy highway, traffic pollution may put you at greater risk of health harm.
  10. People who work or exercise outside face increased risk from the effects of air pollution.
  11. Millions of people are especially vulnerable to the effects of air pollution, including children, older adults and people with lung diseases such as asthma and COPD.
  12. People of color and people with lower incomes are disproportionately affected by air pollution that puts them at higher risk for illness.
  13. Air pollution is a serious health threat. It can trigger asthma attacks, harm lung development in children, and even be deadly.
  14. You can protect yourself by checking the air quality forecast in your community and avoiding exercising or working outdoors when unhealthy air is expected.
  15. Climate change enhances conditions for ozone pollution to form and makes it harder clean up communities where ozone levels are high.
  16. Climate change increases the risk of wildfires whose smoke spreads dangerous particle pollution.
  17. Policymakers at every level of government must take steps to clean the air their constituents breathe.
  18. The nation has the Clean Air Act to thank for decades of improvements in air quality. This landmark law has successfully driven pollution reduction for over 50 years.
  19. Particle pollution exposure from wildfire smoke harms health in ways that range from mild irritation to serious illness and premature death.
  20. Recent updates to the Air Quality Index give the public more accurate information about the health risk from air pollution, and when to take measures to protect themselves on bad air days.
Get More Facts
Take Action