The Rider Trail site off Interstate 70 at Exit 231B, Earth City, is the second air monitoring station in the St. Louis area to provide near-road data. The site is in compliance with the one-hour NO2 standard of 100 parts per billion (ppb). The department began monitoring SO2 at the site in May 2016. Preliminary data show that the site is in compliance with the one-hour SO2 standard of 75 parts per billion (ppb). Both pollutants negatively affect respiration. 


Nitrogen Dioxide

Nitrogen dioxide is a foul-smelling gas. It comes primarily from the burning of fossil fuels — coal, oil and gas. NO2combines with volatile organic compounds (VOCs) in the presence of sunlight and heat to create ozone. (VOCs are compounds with carbon that easily become vapors or gases.)

In 2010, EPA revised the one-hour NO2 standard to 100 parts per billion. An area is in compliance if the design value is at or below the standard. The one-hour standard is based on a three-year design value, which is calculated by taking the 98th percentile of the daily high one-hour average concentrations recorded each year, for three years, and averaging the three years together. The annual standard of 0.053 parts per million is based on the annual arithmetic mean and is not to be exceeded.

Departmental information about nitrogen dioxide (NO2)

  • 2010 standard and related documents

Sulfur Dioxide

EPA not only established a new one-hour standard in 2010, but it also introduced a new form for determining compliance. The new form requires three years of data — the average SO2 concentration from each hour of the year. The department and EPA calculate the design value, using the 99th percentile of one-hour daily maximum concentrations, averaged over three years.

Departmental information about sulfur dioxide (SO2)

  • Description
  • 2010 standard and related documents
Rider Trail I-70 Air Monitoring Site

13080 Hollenberg Drive
Bridgeton, MO 63044
United States

St. Louis
Date Established
Pollutants Monitored
Nitrogen Dioxide
Sulfur Dioxide
38.75264, -90.44884