FAQ

  1. What do the colors mean?
    They are from the Air Quality Index, shown at right. 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. For more information, visit the AIRnow website.

  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. Why is my county missing?
    Most counties don’t have monitors. The state and EPA decide where to place monitors. We report on data gathered in monitors in less than 1,000 of the 3,068 counties in the United States. Counties not included in the report are counties where there are no ozone or particle pollution monitors.

  4. How can I improve my county’s grade?
    Drive less. Use less electricity. 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 your Senators to tell them we need them to support cleaner, healthier air and to oppose measures to block or delay the cleanup of coal-fired power plants.

FACT: Some of the biggest sources of air pollution are dirty power plants, old diesel vehicles and heavy equipment, and ocean-going vessels.

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