Measurements of NH3 and CO2 with distributed-feedback diode lasers near 2.0 µm in bioreactor vent gases
MetadataShow full item record
Measurements of NH3 and CO2 were made in bioreactor vent gases with distributed-feedback diode-laser sensors operating near 2 um. Calculated spectra of NH3 and CO2 were used to determine the optimum transitions for interrogating with an absorption sensor. For ammonia, a strong and isolated absorption transition at 5016.977 cm-1 was selected for trace gas monitoring. For CO2, an isolated transition at 5007.787 cm-1 was selected to measure widely varying concentrations [500 parts per million (ppm) to 10%], with sufficient signal for low mole fractions and without being optically thick for high mole fractions. Using direct absorption and a 36-m total path-length multipass flow-through cell, we achieved a minimum detectivity of 0.25 ppm forNH3 and 40 ppm for CO2. We report on the quasi-continuous field measurements of NH3 and CO2 concentration in bioreactor vent gases that were recorded at NASA Johnson Space Center with a portable and automated sensor system over a 45-h data collection window.
When this research was performed, M. E. Webber, J. B. Jeffries and R. K. Hanson were with the High Temperature Gasdynamics Laboratory, Department of Mechanical Engineering, Stanford University. M. E. Webber is now with Pranalytica, Inc. When this research was performed, R. Claps, F. V. Englich, and F. K. Tittel were with the Laser Science Group, Rice Quantum Institute, Department of Electrical and Computer Engineering, Rice University. R. Claps is now with Radiant Photonics, Inc.