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 roughly 1,000 counties throughout 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 an email to EPA to tell them we need tighter, more protective ozone and particle pollution standards.

FACT: Twenty-five of the top 27 most-polluted cities for year-round particle pollution levels had cleaner air than last year’s report found.

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SOTA 2011 Survey