City Air Quality

This database reports nine air quality trends for Core-Based Statistical Areas (CBSAs).  Trend data are based on sites having an adequate record of monitoring data during the trends period. Data meet the EPA's air quality “trend” criteria, listed below. There are PM2.5 data quality issues that affect Florida, Illinois, most of Tennessee and parts of Kentucky, and the EPA has removed these data.  

See category definitions and the EPA's air trends for additional information. 

EPA Air Quality Trend Criteria

• Meet completeness criteria for each measure as indicated:
• 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.
• Include exceptional events after 2011 (exceptional events were excluded prior to 2011 if concurred by EPA Regional Offices).
• Require that at least 75% valid years over the trend period and that no more than two consecutive years of data are missing.
• Exclude point-source sites for Lead maximum rolling 3-month average.
• Use only filter-based Federal Reference Method (FRM) data per Air Quality Standard (AQS) parameter 88101 for PM2.5 metrics use; other FEM data from continuous monitors (AQS parameter 88502) are not included.
• Contain only the most complete, measured by number of valid years, for multiple monitoring sites in the same CBSA.
• Interpolate data for missing years.