AIRBORNE MEASUREMENTS OF AEROSOL OPTICAL-PROPERTIES OVER SOUTH-CENTRAL NEW-MEXICO

We used a three wavelength nephelometer (449, 536 and 690 nm) and an a ethalometer on board the NOAA King Air research aircraft to assess the contributions of aerosol optical scattering and absorption to shortwa ve extinction. The measurements were made over south-central New Mexic o in February and July 1989. The winter measurements revealed a shallo w, polluted planetary boundary layer with cleaner air above. The summe r measurements showed a uniformly mixed planetary boundary layer exten ding from ground level to the operational ceiling of 4.5 km above grou nd. In both cases the total optical thickness values for the column we re similar (0.03) and the fractional contribution of aerosol absorptio n to the extinction was between 5 and 10%. These results suggest that the aerosol extinction in summer and winter is similar, even though th e planetary boundary layer thickness is quite different during the two seasons. They also demonstrate that a suitably instrumented light air craft can profile the optical properties of the troposphere with high sensitivity and good spatial resolution.