Emissions and Opacity Monitoring

Picture of smoke stack with CEMS COMS equipment attached.

Continuous Emission Monitoring Systems (CEMS) and Continuous Opacity Monitoring Systems (COMS) involve the installation of monitoring equipment which accumulates data on a pre-determined time schedule in a stack or duct.   Many of the principles of stack testing also apply to continuous monitoring systems. The difference is that the stack test is for a relatively short time period (hours), while the CEM/COM covers longer periods of time such as months or years. 


Continuous measurements provide data under all facility operating conditions.   These data can be used both by the facility and by regulatory agencies and can be accessed by the public.   The regulatory uses of continuous monitoring data provide so many advantages to environmental control agencies that federal and state continuous monitoring requirements have been steadily increasing since the 1970s. Public awareness of environmental pollution, especially the release of toxic pollutants, is increasing.   Continuous monitoring systems are used to provide assurance that a facility is not emitting pollutants in excess of its standards.  CEMS/COMS are required on a given source are the best and quite often the only way for the facility and the regulatory agency to determine compliance with emission limits. 


Technical Assistance Resources 

Guidance for Continuous Opacity and Emission Monitoring Systems - This guidance document explains the planning, installation, certification, testing, and reporting requirements for continuous emission and continuous opacity monitoring systems, and is a support document for the Air Quality Division, Compliance Support Unit's existing continuous emission and opacity monitoring procedures. The fact sheet also includes a new Monitoring Plan Form (EQP 5739) to detail the on-site installation of a continuous emission or opacity monitor, and a compliance checklist that covers the steps needed for minimum continuous opacity and emission monitor compliance.

"Continuous Opacity and Continuous Emission Monitoring Systems" Fact Sheet  - (February 1998)

Monitoring Plan for Continuous Opacity Monitors (COMS) and Continuous Emission Monitors (CEMS)- (February 1998) 

Checklist for "Compliance of Continuous Emission Monitors (CEMS) and Continuous Opacity Monitors (COMS)"- (February 1998) 


For More Information or Additional Assistance, contact the
Environmental Assistance Program  at 800-662-9278 

Do you have an outreach idea or suggestion for our Program?  Please feel free to submit your requests to: David Fiedler.