Continuous emissions monitoring or CEM is the continuous measurement of pollutants emitted into the atmosphere in exhaust gases from combustion or industrial processes. CEM is the commonly used term to describe instantaneous or real-time environmental monitoring of gases and particulate matter that pass through flues, ducts and chimney stacks etc. CEM is also known as Stack Gas Monitoring or Flue Gas Monitoring.

There are two main drivers for Continuous Emissions Monitoring. The first (and by far the main requirement) is to demonstrate compliance with Environmental Legislation such as IPPC and the second is for Process Control (i.e. combustion efficiency).

There are hundreds of CEM applications, below are listed the most common:
Waste Incineration (Municipal, Clinical, Hazardous, Pharmaceutical)
Large Power Plant (Coal and Oil fired)
Small-Medium Power Plant (Gas turbine)
Chemical Plants
Oil Refineries
Cement Plants
Brick Plants
Mineral Wool Plants
Aluminium Smelters
Acid Plants