There is a growing need to develop improved technologies for precise airborne measurements of carbon dioxide, CO2. CO2 measurements are of great importance to many areas of research, including climate change, global carbon budgets, and geological research in relation to volcanic activity. At the same time, we are entering a period of time in which Unmanned Aircraft Systems (UAS) are becoming more widely used for atmospheric research. UAS platforms have already proven themselves as a uniquely capable means for making measurements in remote areas and over oceans. However, existing CO2 measurement technologies are difficult to adapt to or use in the UAS world. This proposal describes a simple and inexpensive sensor for the precise determination of atmospheric CO2 that will be small enough for flight on small UAS platforms and sounding balloons. Phase I will include the fabrication of a proof-of-concept sensor system, laboratory characterization of the sensor, and culminate in a demonstration of the sensor on a UAS. Phase II will emphasize improving the basic manufacturability of the design, as well as much more extensive laboratory and UAS testing.