AN OPEN PATH DIODE LASER FLUX METER FOR TRACE GASES OF BIOGENIC ORIGIN

THE PURPOSE OF THIS PROJECT IS TO DESIGN AND DEVELOP AN INSTRUMENT TO MEASURE FLUXES OF TRACE GASES IN ORDER TO DETERMINE THEIR SOURCES AND SINKS IN THE BIOSPHERE. THE METHOD IS BASED ON THE WELL ESTABLISHED EDDY CORRELATION TECHNIQUE AND WOULD USE A TUNABLE DIODE LASER SOURCE COMBINED WITH A UNIQUE OPEN PATH MULTIPLE PASS ABSORPTION CELL FOR TRACE SPECIES DETECTION AT SUB-PPB LEVELS. THIS INSTRUMENT WILL HAVE THE FAST TIME RESPONSE (0.1 S) AND SHORT MEASUREMENT PATH (1 M) REQUIRED FOR THE EDDY CORRELATION METHOD. IN THE PHASE I STUDY, THE OPEN PATH ABSORPTION CELL WILL BE DESIGNED, ASSEMBLED, AND TESTED IN ORDER TO VALIDATE THE MEASUREMENT CONCEPT AND DEFINE SENSITIVITY LIMITS. THESE TESTS WILL BE CONDUCTED IN COMBINATION WITH A LABORATORY TUNABLE DIODE LASER SYSTEM AND WILL INCLUDE OPEN PATH MEASUREMENTS OF TRACE GASES SUCH AS NITROUS OXIDE. OPTIMUM DETECTION WAVELENGTHS FOR SEVERAL GASES WILL BE DETERMINED IN THE PHASE I PROGRAM, INCLUDING NITROUS OXIDE, METHANE, CARBON MONOXIDE, AMMONIA, CARBONYL SULFIDE, AND CARBON DISULFIDE. THE RESULTS OF THE PHASE I EFFORT ARE EXPECTED TO RESOLVE CRITICAL DESIGN ISSUES AND PERMIT THE DEVELOPMENT OF AN INSTRUMENT FOR FIELD USE IN PHASE II.