Missouri and Illinois calculate eight-hour ozone averages based on monitored data and identify days which had a maximum eight-hour average of 85 ppb or greater. 

OZONE MONITORS AS OF APRIL 2006 1. Arnold (formerly Arnold Tenbrook) 2. Orchard Farm 3. West Alton 4. Maryland Heights 5. Pacific 6. Sunset Hills 7. Blair 8. Margaretta 9. Wood River (formerly 54 Walcott) 10. Maryville (formerly 200 W. Division) 11. Alton (formerly 409 Main St.) 12. East St. Louis (formerly 13th & Tudor) 13. Jerseyville (eight-hour ozone info.)

Listed below are tables presenting the maximum eight-hour ozone value by monitor.  These tables present, on a weekly basis, the highest eight-hour average by monitor starting with 1999 and beginning in 2004 the four highest eight-hour ozone averages by monitor. The measurement unit is parts per billion.

For 1999-2000 eight-hour ozone information is available for a monitor located on St. Charles Rock Rd. in St. Ann. In 2001 this monitor was moved to the Breckenridge Hills site.

For 1999 eight-hour ozone information is available for a monitor located at Newstead and Cote Brilliante in the City of St. Louis. In 2000 this monitor was moved to the Margaretta site.

For 1999-2003 eight-hour ozone information is available for a monitor located on S. Broadway in the City of St. Louis. In 2004 this monitor was shut down.

As of April 2005, monitors at the following sites have either been deactivated or relocated to another location: Breckenridge Hills (data available 2001-2004); Ferguson (1999-2004); Ladue (1999-2004); Clark in the City of St. Louis (1999-2004); and Edwardsville (1999-2004). New monitor locations in 2005 are Maryland Heights, Pacific and Blair Street in the City of St. Louis.

As of April 2006, the monitor at the Queeny Park site has been deactivated. Data is available for the period 1999-2005.

Weekly Tables Presenting Eight-Hour Ozone Averages by Monitor