Address: General Electric store, Highway 94,
               next to fire station
               West Alton, MO 63386
County: St. Charles
Date established: Nov. 1, 1968
Pollutant monitored: Ozone (O3)
Pollutants no longer monitored: NO2, SO2, PM10, PM2.5
    For information, go to dnr.mo.gov/sunshinerequests.htm.
Site coordinates
   * Latitude: 38.8725°
   * Longitude: -90.226389°

Ozone (O3) Data*

The federal ozone season runs from March 1 through October 31.
Ground-level ozone forms when pollutants emitted by cars, factories, power plants and other sources react chemically in the presence of heat and sunlight. Ozone at ground level is a harmful air pollutant as opposed to ozone in the upper atmosphere, which protects us from ultraviolet light.

As of 2015, the federal standard for ground-level ozone is 70 parts per billion, or 0.070 parts per million. An area is in compliance if the design value is at or below this standard. A design value for ozone incorporates data from three years. The department and EPA calculate the design value by 1) ranking the daily eight-hour ozone
values for three consecutive years; 2) extracting the fourth-highest value for each year; and 3) averaging the three figures.

Weekly summary of preliminary data from all ozone sites

  • Eight-hour ozone design values
  • Four highest eight-hour ozone values since beginning of ozone season
  • Exceedances during current ozone season
  • Daily eight-hour average maximums since beginning of ozone season

Preliminary one-hour averages from West Alton

  • Ozone data in third and fourth columns. "P" stands for primary monitor. "S" stands for secondary monitor
  • Data from 10 days ago through current date
  • Central Standard Time
  • Concentration of ozone in parts per million (ppm)

Preliminary eight-hour forward-rolling averages from all ozone sites

  • Hourly data equal to average of that hour and the following seven hours
  • Data from 10 days ago through current date
  • Central Standard Time
  • Concentration of ozone in parts per million (ppm)

Preliminary one-hour ozone averages from all sites

  • Data from 10 days ago through current date
  • Central Standard Time
  • Concentration of ozone in parts per million (ppm)

2016 list of exceedances

Graph of design values for ozone sites in the St. Louis area, beginning in 2003

Additional information about ground-level ozone

*Technical issues can affect ability to deliver quality data.
Access a table of symbols indicating technical issues

Related Links

Missouri's network of air monitoring sites on interactive map

National standards for pollutants

Real-time views from cameras in Kansas City, St. Louis

Daily Air Quality Forecast (AirNow) shows how current readings
at air monitoring sites rate on the EPA's Air Quality Index.
* Click on Missouri in the state box at the top of the home page
to access information.

EPA Air Toolbox for Citizen Scientists