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FAQ

Chart of air quality colors

  1. What do the colors mean? 
    They are from the Air Quality Index, shown above. We compare the monitored data against the Air Quality Index, a color-coded scale that EPA developed to help the public understand daily air pollution forecasts and protect themselves. Each color provides a specific warning about the risk associated with air pollution in that range. Learn more about the Air Quality Index. Find more information about the amount of pollution at each range in the Methodology.
  2. How do we calculate the grades? 
    In our analysis of ozone and short-term levels of particle pollution, we assign increasing weights to the days when air pollution levels reach the higher ranges to calculate our grades. We add those together and calculate the weighted average, then assign grades based on that weighted average. For year-round levels of particle pollution, we use annual average levels calculated by EPA. For more details, view our Methodology.
  3. What does DNC mean? 
    DNC means "Data Not Collected." Most counties don't have monitors. The state and EPA decide where to place monitors. Monitors are located in less than 1,000 of the 3,068 counties in the United States. Counties where the grade shows "DNC" are counties where no monitors exist to collect information about that pollutant.
  4. What does INC mean? 
    INC means "Incomplete." A county needs three years of data to adequately compare levels of pollution with national standards.  If the county lacks three years of data, then the information is listed as "incomplete."
  5. How can I improve my county's grade? 
    Drive less. Use less electricity. Don't burn wood or trash.  Support measures in your community that can cut air pollution. Tell your local and state officials to take steps to clean up air pollution. Send a message to Congress to tell them we need them to support cleaner, healthier air. Find more suggestions here for what needs to be done.

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