The aim of this proposal is to develop a low power consuming solid polymer electrolyte based, miniaturized electrochemical CO2 sensor that can continuously, accurately and rapidly monitor CO2 concentrations in closed or nearly closed environments for monitoring and control approaches for plant-production environments, to aid in NASA?s biomass (edible food) production research. The proposed sensor will introduce a much simpler, lower cost and more accurate alternative to the existing infrared CO2 measurement technology to measure CO2 and study its effects on plant growth. During Phase I, in addition to concept feasibility demonstration, the ability of the proposed sensor to detect (0 - 10) % CO2 in a wide temperature (15 ? 45) oC, and humidity (10 ? 99) % RH will be demonstrated. The proposed sensor will be evaluated for its fast response and continuous and uninterrupted operation for 100 hours. In Phase II the sensor will be integrated into a complete instrument, which will be small, lightweight and will allow for independent operation of the sensor complete with calibration routine, adjustable applied potential settings and digital display of numeric results. The unit will be battery operated with an AC converter and battery re-charger.