This Small Business Innovative Research Phase I proposal seeks to develop an ultrasensitive, multispecies sensor system for use in determining the efficacy of air revitalization systems in space vehicle environments such as the International Space Station (ISS). The proposed instrument will be capable of determining absolute concentrations of numerous target molecules in real time, including CO2, CH4, H2O, NH3, and CO. Aside from CO and NH3, these species will be monitored with a precision and accuracy of 0.1% for commonly encountered levels. The detection limits (S/N=2) for CO and NH3 will be 50 and 5 ppbv, respectively. This compact, lightweight instrument will be capable of long-term unattended operation, and require minimal power. The Phase I research will demonstrate the feasibility of the technology by performing measurements on priority targets using a bench-scale laboratory instrument that employs a single, frequency agile laser source. The results of these tests will be used to quantify detection limits for a Phase II instrument that will employ a multiplexed diode-laser configuration. The proposed system will be capable of rapidly detecting numerous species with high precision and specificity. Commercial systems based on the Phase II prototype will be developed and marketed during Phase III.