Ozone Monitoring

One component for measuring the effectiveness of local air pollution control programs is the ongoing collection of ozone data generated by a network of 10 air pollutant monitors located throughout the St. Louis region.

Ozone Data Sharing Project

East-West Gateway Council of Governments (EWG) staff serve as a clearinghouse for daily measured ozone data and helps to insure quality control on all monitored data assembled from the regions network of monitors. EWG collects one-hour ozone data and eight-hour ozone averages from the Missouri Department of Natural Resources (MoDNR) and the Illinois Environmental Protection Agency (IEPA). The one-hour data is examined for problems and missing values and is entered into a computer spreadsheet program. Missouri and Illinois states use the one-hour concentrations to calculate eight-hour averages for each monitor and identify the days and monitors which have exceeded the standard.  Staff records the maximum eight-hour average by monitor by day in a spreadsheet program. Weekly and monthly summary reports are prepared by staff and forwarded to the monitoring agencies and the U.S. Environmental Protection Agency (EPA).

2018 Ozone Information

Air Quality Index

The EPA-developed Air Quality Index (AQI) is designed to help inform the public about air pollution levels in their area and the associated health impacts.

What is the AQI?

The AQI presents standardized information on air quality. Ozone and fine particulate matter (PM2.5) forecasts and information are available on the EPA’s AirNow website. MoDNR also produces a St. Louis Visual Air Pollution Camera.

To obtain the AQI for a particular day, the maximum 8-hour average is entered into EPA’s AQI conversion calculator. Ozone values in the AQI run from 0 (satisfactory) to 500 (hazardous). An AQI value of 100 corresponds to the National Ambient Air Quality Standard established for a pollutant.

AQI Calendars

The EWG AQI Calendar graphically presents the ozone AQI for March-October. The daily AQI is plotted into its respective color code (i.e., green for good, yellow for moderate, etc.) in the calendar. It can be used to instantly observe the ozone season and the various ozone episodes and their severity. AQI Calendars for 2015 through 2018 can be found below.

Ozone Monitoring Data

Eight-Hour Ozone Averages by Monitor

Missouri and Illinois calculate eight-hour ozone averages based on monitored data and identify days which had a maximum eight-hour average of 71 parts per billion (ppb) or greater.  The eight-hour ozone averages for 2015 through 2018 can be found below.

One-Hour Ozone Averages by Monitor

EWG collects one-hour ozone data from the monitoring agencies for the previous day covering the period 9 a.m. to 9 p.m. CST.  The one-hour ozone data for 2015 through 2018 can be found below.

Looking for AQI Calendars or Ozone Averages from Prior Years?

EWG’s Library contains important agency documents including those from prior years.  Use the link below to access AQI calendars from 2001 through 2014, the eight-hour ozone averages from 1999 through 2014, and the one-hour ozone averages from 1998 through 2014.

AQI Calendars 8-Hour Ozone Averages 1-Hour Ozone Averages


Contact EWG staff by phone at (314) 421.4220 or (618) 274.2750 or by email at AirQuality@ewgateway.org.