A NITRIC ACID DRY DEPOSITION EDDY CORRELATION FLUXMETER

NITRIC ACID IN THE GAS PHASE IS ONE OF THE MOST ABUNDANT TRACE NITROGEN OXIDE SPECIES IN THE ATMOSPHERE. ITS DEPOSITION AT THE SURFACE PROVIDES THE MAJOR SINK FOR NOX AND IS A SIGNIFICANT COMPONENT OF ACID PRECIPITATION. THE GOAL OF THIS PROJECT IS TO DEVELOP AN INSTRUMENT TO MEASURE THE SURFACE FLUXES OF NITRIC ACID USING THE EDDY CORRELATIONTECHNIQUE WITH INFRARED TUNABLE DIODE LASER ABSORPTION FOR THE DIRECT DETECTION OF HNO3. THE INSTRUMENT USES A NOVEL, MULTIPLE-PASS ABSORPTION CELL THAT MAXIMIZES THE OPTICAL PATHLENGTH IN A MINIMAL VOLUME TO PROVIDE SUFFICIENT TIME RESPONSE (0.1 SEC) FOR EDDY CORRELATION MEASUREMENTS. A KEYCOMPONENT OF THE SYSTEM IS THE DESIGN OF A SUPERSONIC INLET THAT WILL MINIMIZE THE EFFECTS OF SURFACE ABSORPTION AND DESORPTION ON THE WALLS OF THE INLET AND DETECTOR. THE PHASE I STUDY WILL OPTIMIZE AND TEST THE SAMPLING CELL TIME RESPONSE AND WILL RESOLVE CRITICAL DESIGN ISSUES LEADING TO THE DEVELOPMENT OF A FIELD INSTRUMENT FOR HNO3 DETECTION AT THE 100 PPT LEVEL IN PHASE II. THE FINAL INSTRUMENT WILLALSO BE APPLICABLE TO FLUX MEASUREMENTS OF OTHER REACTIVE TRACE GASES INCLUDING SULFUR DIOXIDE, NITRIC OXIDE, OZONE, AMMONIA, AND HYDROGEN PEROXIDE.