AIRBORNE LASER-INDUCED FLUORESCENCE SYSTEM FOR MEASURING OH AND OTHER TRACE GASES IN THE PARTS-PER-QUADRILLION TO PARTS-PER-TRILLION RANGE

Described in detail is a laser induced fluorescence system which has been successfully interfaced with two aircraft sampling platforms (i.e., Sabreliner jet and an L-188C Electra). This system, which has been under development for four years, presently consists of the following major components: (1) a Nd-Yag laser driven oscillator-amplifier dye laser; (2) a sampling manifold with associated fluorescence detection optics; (3) an OH calibration chamber; (4) a laser beam steering assembly; and (5) sampling electronics and data processing hardware. During the last three years, this system has been flown some 50000 air miles making tropospheric OH radical measurements over the latitude range of 70°N to 57°S. OH concentrations measured during these flights have ranged from 30 parts-per-quadrillion (3.7×105 molecules/cm 3) at altitudes of 6 km to 0.8 parts-per-trillion (2.0×10 7 molecules/cm3) at 0.5 km. Computations have been completed which indicate that the existing aircraft system with modest modifications should also be capable of detecting natural tropospheric levels of NO, SO2, CH2O, NO2, HNO2, NO 3, H2O2, and CS2 by using both conventional laser-induced fluorescence methodology and multiphoton techniques.