Knowledge Bank

We have demonstrated the technical feasibility of an analyzer for determining nitric oxide (NO) concentrations in stack gases using a carbon monoxide laser. The analyzer is based on the selective absorption by NO of one of the emission lines lines available from a CO laser. The absorption is due to a single rotational line of the fundamental vibration-rotation band of NO near $5\mu$m. In the past, attempts to utilize this region for NO determination using conventional spectroscopic techniques have proved impractical due to interference from other gases, principally water vapor and carbon dioxide The extremely high resolution possible using laser spectroscopy is the key to eliminating the interference from other gases. We have determined that the P(15) line of the 7-6 vibrational band at $1927.282cm-1$ provides good selectivity for NO. At this frequency the absorption coefficient of NO measured in the presence of water vapor at a temperature between 400 and $450\circ K$ has a value of $330cm-1atm-1$. Under the same conditions the measured absorption coefficient for water vapor is $0.2m-1atm-1$. The absorption coefficient of all other common stack gases is negligible. We shall discuss the effect on the accuracy of the NO measurement of variations in temperature, water vapor, and particle concentration.