Continuous emission monitoring systems (CEMS) were historically used as a tool to  

monitor flue gas for oxygen, carbon monoxide and carbon dioxide to provide information 

for combustion control in industrial settings. They are currently used as a means to comply  

with air emission standards such as the local Environmental Protection Agency's 

 Regulation. Facilities employ the use of CEMS to continuously collect record and r eport

the required emissions data. 

The standard CEM system consists of a sample probe, filter, sample line (umbilical), gas 

conditioning system, calibration gas system, and a series of gas analyzers which reflect 

 the parameters being monitored. Typical monitored emissions include: sulfur dioxide,

nitrogen oxides, carbon monoxide, carbon dioxide, hydrogen chloride, airborne particulate 

matter, mercury, volatile organic compounds, and oxygen. CEM systems can also  

measure air flow, flue gas opacity and moisture.