A TUNABLE LASER BASED MONITOR FOR ATMOSPHERIC HO2

THE HYDROPEROXYL RADICAL (HO2) IS AN IMPORTANT ATMOSPHERIC TRACE SPECIES WHICH PARTICIPATES IN THE FORMATION AND DESTRUCTION OF OZONE IN BOTH THE TROPOSPHERE AND THE STRATOSPHERE. TOGETHER WITH THE HYDROXYL RADICAL (OH) IT FORMS CATALYTIC CYCLES WHICH RESULT IN THE OXIDATION OF COMPOUNDS RELEASED AT THE SURFACE OF THE EARTH AND THUS PROVIDES THE MAJOR CLEANSING MECHANISM FOR HYDROCARBONS AND MAN-MADE POLLUTANTS IN THE LOWER ATMOSPHERE. THIS PROPOSAL IS TO DEVELOP AN INSTRUMENT CAPABLE OF MEASURING THE CONCENTRATION OF TROPOSPHERIC HO2 DIRECTLY, USING TUNABLE INFRARED DIODE LASERS. THE PROPOSED INSTRUMENT WOULD USE A NOVEL MULTIPASS CELL WHICH MAXIMIZES THE OPTICAL PATH-LENGTH WHILE MINIMIZING THE CELL VOLUME AND THEREFORE ALSO THE HO2 RESIDENCE TIME AND WALL LOSS. THE PHASE I EFFORT WILL FOCUS ON TESTING A PROTOTYPE MULTIPASS CELL AND ON CHOOSING THE BEST SPECTRAL REGION FOR MONITORING HO2. THIS EVALUATION WILL BE BASED, IN PART, ON HO2 PRESSURE BROADENING COEFFICIENTS WHICH WILL BE MEASURED IN PHASE I. IN PHASE II, WE WOULD INTEGRATE THE MULTIPASS CELL INTO A FIELD INSTRUMENT CAPABLE OF MEASURING TROPOSPHERIC HO2 AT CONCENTRATIONS EXCEEDING 10 PPTV.