County Air Quality

This database contains 13 air quality measures for all U.S. counties.  Monitoring data represent the quality of air in the vicinity of the monitoring site and, for some pollutants, may not necessarily represent urban-wide air quality.  Data meet the EPA's air quality "completeleness" criteria, listed below.  These summaries are not adequate to numerically rank counties according to their air quality.  

There are data quality issues that affect Florida, Illinois, most of Tennessee and parts of Kentucky, and the EPA has removed these data.  For additional information, see Air Data.

• U.S. EPA Completeness Criteria
• CO 2nd highest non-overlapping 8-hour average: >= 3,285 hourly observations
• Lead maximum rolling 3-month average: >= 9 valid rolling 3-month averages in year
• NO2 annual mean of 1-hour: >= 4,380 hourly observations
• NO2 98th percentile of daily maximum 1-hour: >= 75% hours in a day; >+ 75% days in quarter for all four quarters
• Ozone 4th highest daily maximum 8-hour average: >= 50% of hourly observations
• PM10 2nd highest 24-hour average: >= 30 daily observations
• PM2.5 weighted (by quarter) annual average: >=11 daily observations for all four quarters
• PM 2.5 98th percentile of daily average: >=11 daily observations for all four quarters
• SO2 99th percentile of daily maximum 1-hour: >= 75% hours in a day and >= 75% days in a quarter for all 4 quarters.