FAST RESPONSE INSTRUMENTATION FOR METHANE FLUX MEASUREMENTS

METHANE PLAYS AN IMPORTANT ROLE IN THE CHEMISTRY OF BOTH THETROPOSPHERE AND STRATOSPHERE, AND ITS INCREASING CONCENTRATION MAY HAVE IMPORTANT EFFECTS ON THE GLOBAL ENVIRONMENT. THE DEVELOPMENT OF IMPROVED LOW COST INSTRUMENTATION FOR REAL-TIME MEASUREMENT OF METHANE FLUXES IS CRUCIAL TO CHARACTERIZING THE SOURCES AND SINKS OF THIS IMPORTANT ATMOSPHERIC SPECIES. THIS PROJECT WILL DEVELOP NEW INSTRUMENTATION BASED ON NEAR-INFRARED ABSORPTION USING AN INEXPENSIVE AND HIGHLY RELIABLE ROOM TEMPERATURE LASER DIODE AS THE LIGHT SOURCE. AN EXCEPTIONALLY RUGGED AND COMPACT INSTRUMENT FOR FIELD USE CAN BE DESIGNED USING FIBEROPTICS IN PLACE OF MOST CONVENTIONAL OPTICS. USE OF HIGH FREQUENCY LASER MODULATION AND DETECTION METHODS SHOULD PROVIDE A SENSITIVITY OF 1% OF THE AVERAGE AMBIENT METHANE CONCENTRATION, WITH 10 HZ RESPONSE. A FURTHER ADVANTAGE OF THIS METHOD IS THAT SIMULTANEOUS WATER VAPOR MEASUREMENTS CAN BE MADE WITH THE SAME INSTRUMENT; THIS ALLOWS METHANE MEASUREMENTS TO BE CORRECTED AUTOMATICALLY TO DRY AIR MIXING RATIOS. IN PHASE I A BREAD-BOARD INSTRUMENT WILL BE ASSEMBLED AND TESTED TO DETERMINE SENSITIVITY, CALIBRATION STABILITY, AND ACCURACY OF THIS APPROACH. PHASE I EXPERIMENTS WILL INCLUDE MEASUREMENTS OF METHANE AND WATER VAPOR IN LOCAL AMBIENT AIR. THESE RESULTSWILL PROVIDE THE BASIS FOR THE PHASE II DEVELOPMENT OF A PROTOTYPE INSTRUMENT FOR USE IN FIELD STUDIES.