Infrared Spectrometry
Identifies specific gas 
Not subject to interference from other gases
Long term calibration stability
Multiple detection points per detector
Detects multiple gases at a specific point
Can monitors integrity of air sampling tube
Most accurate detection
Provides IR spectrum for reference and verification 
of unknowns
High initial capital investment
Significant lag time between samples
Will not detect atomic or diatomic gases that do not adsorb infrared radiation (e.g. Oxygen (O2), Chlorine (CL2), Fluorine (F2), and Hydrogen (H2))