Computer Automation and Error Analysis of a CO2-Laser Long-Path Absorption System for Air Pollution Monitoring

A CO2-laser long-path absorption system for air pollution monitoring has been computer automated. Both the lasers and the electronic circuits are controlled by a computer. Real-time estimation of both systematic error and imprecision is used to select an optimum measurement strategy for each different pollution situation expected. The system has been used in a field experiment in the vicinity of a petrochemical industry where ethylene and vinyl chloride are produced. Ethylene concentrations from below 30 up to 400 ppb were monitored using path lengths of 500-2800 m. The concentrations of vinyl chloride were generally small (< 50 ppb). The systematic errors of the measurements were typically 5-10 percent and the imprecision 5-25 percent.