A DIODE LASER-BASED DIRECT GRADIENT SENSOR FOR MONITORING ATMOSPHERIC DRY DEPOSITION

THE PURPOSE OF THIS STUDY IS THE DEVELOPMENT OF INSTRUMENTATION TO MEASURE DRY DEPOSITION RATES OF ATMOSPHERIC TRACE GASES. THE METHOD IS BASED ON THE CONCENTRATION GRADIENT TECHNIQUE AND WILL USE A TUNABLE DIODE LASER LIGHT SOURCE COMBINED WITH LONG LINE-OF-SIGHT ABSORPTION PATHS TO DETECT TRACE SPECIES AT PART-PER-BILLIONCONCENTRATIONS. THE INSTRUMENT WILL BE DESIGNED SPECIFICALLY FOR THE DIRECT MEASUREMENT OF CONCENTRATION DIFFERENCES (GRADIENTS) ALONG MULTIPLE PATHS AT DIFFERENT HEIGHTS ABOVE THE GROUND, USING A DUAL BEAM OPTICAL ARRANGEMENT WITH A NOVEL METHOD OF SIGNAL PROCESSING TO OBTAIN HIGHLY ACCURATE MEASUREMENTS. IN PHASE I, A METHOD FOR STABILIZING THE OUTPUT OF THE DIODE LASER USING OPTICAL FEEDBACK, WHICH IS THE KEY COMPONENT OF THE DIFFERENTIAL MEASUREMENT METHOD, WILL BE DEVELOPED AND TESTED. THE RESULTS OF PHASE I ARE EXPECTED TO RESOLVE CRITICAL DESIGN ISSUES AND PERMIT THE DEVELOPMENT OF A SIMPLE YET RUGGED FIELD INSTRUMENT IN SUCCEEDING PHASES. THE INSTRUMENT WILL BE APPLICABLE TO FLUX MEASUREMENTS OF TRACE GASES INCLUDING SULFUR DIOXIDE, NITRIC OXIDE, NITROGENDIOXIDE, NITRIC ACID, OZONE, AND HYDROGEN PEROXIDE.