Department staff member checking an air monitoring station in Liberty.

Missouri operates a network of about 50 ambient air monitoring sites. The department maintains a web page with additional information for each of these sites, link found below.

Air monitoring is required by the U. S. Clean Air Act. Details on siting and operation of air monitoring sites and on operation of air monitoring instruments in a way to ensure that the data collected are valid are found in federal regulations in Title 40 of the Code of Federal Regulations (40 CFR), “Protection of Environment,” primarily in parts 50 and 58 of 40 CFR.

A primary purpose of this air monitoring network is to determine whether areas in Missouri are meeting the primary National Ambient Air Quality Standards (NAAQS). These standards are established by EPA to protect human health effects. Data from the monitoring network are sent to EPA’s national database of air monitoring data, called the Air Quality System (AQS). An additional primary purpose of this air monitoring network is to help develop information on air quality for the citizens of Missouri. Concentrations of most air pollutants are measured continuously, with hourly averages reported. The department develops multiple plans available within the state planning webpage to meet federal standards for six criteria pollutants; lead, ozone, particulate matter, carbon monoxide, nitrogen dioxide and sulfur dioxide. 

A detailed description of the network and demonstration that it is intended to meet all the ambient air monitoring requirements in 40 CFR are included in the monitoring network plans mentioned below. The plans are updated annually, posted on the internet for public review, and sent to EPA for approval.

In addition to the basic required monitoring sites, called State and Local Air Monitoring Stations (SLAMS), Missouri operates special purpose monitors (SPM), for example, for short term air quality studies of air quality or instrument evaluation and monitors for trends in concentrations of toxic air pollutants at a site in St. Louis as a part of the National Air Toxics Trends Sites (NATTS) network.

In addition to monitoring done by the state, some industrial facilities in Missouri conduct air monitoring near their facilities. This monitoring is done following quality assurance requirements reviewed and approved by the state, and site operation and instrument performance at these sites are periodically reviewed (audited) by the state. These industrial sites are also identified in the annual monitoring network plan. Data from these sites are also reported to the AQS database.

Air Toxics

A group of 187 other air pollutants called hazardous air pollutants are address by section 112 of the Clean Air Act. Although these pollutants are found in the ambient air, there are no federal ambient air quality standards set to address these pollutants. Instead, federal rules are established to place emissions standards, or requirements, on sources of hazardous air pollutants called new source performance standards. These standards place national emission standards for hazardous air pollutants for 174 named categories of sources that emit hazardous air pollutants to the air. Missouri monitors long-term air toxics trends in the ambient air at one site in St. Louis City and implements a permitting program for major sources of hazardous air pollutants.

Monitoring Network Assessments

The department is required to submit an assessment of the air quality monitoring network every five years to EPA. The assessment helps the state determine whether the network meets the monitoring objectives defined in 40 CFR 58 Appendix D, whether new sites are needed, whether existing sites are no longer needed, and whether new technologies are appropriate for incorporation into the monitoring network. This assessments follow EPA Region 7 guidance. Recent changes or proposed changes in the National Ambient Air Quality Standards (NAAQS) must be considered in assessing the air quality monitoring network.

The assessment discusses Missouri population, climate and new emission sources that are used to evaluate the network for monitoring of each of the following air pollutants: carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2), particulate matter smaller than 10 micrometers (PM10), ozone (O3), particulate matter smaller than 2.5 micrometers (PM2.5) and lead. 

Monitoring Network Annual Plans

The department is required to produce and submit annual monitoring network plans to EPA to ensure each monitor meets federal and state requirements. The plan must contain specific information regarding each air monitoring site such as location, operating schedule, identification numbers, sampling and analysis methods.