VERTICAL-DISTRIBUTION OF ATMOSPHERIC AEROSOL-SIZE DISTRIBUTION OVER SOUTH-CENTRAL NEW-MEXICO

The vertical distribution of background atmospheric aerosols was measu red over south-central New Mexico as a part of the Atmospheric Lidar V erification Experiment (ALIVE) during four research field periods in t he summers and winters of 1989 and 1990. Aerosol size distribution was measured from the surface up to 4500 m above sea level (asl) over the particle size range 0.1 approximately 32 mum, using two Particle Meas uring Systems (PMS) probes mounted on the wings of the NOAA King Air r esearch aircraft. Vertical profiles of aerosol number concentrations o f both fine- (0.1-2.0 mum) and coarse- (> 2.0 mum) particle modes show seasonal differences, with higher number concentrations and higher mi xed layer heights during summers. The measured aerosol size distributi on data of each ALIVE intensive were averaged for boundary layer and f ree troposphere regions. These data mostly exhibit bi-modal distributi ons, typical for the continental atmospheric aerosols. Exceptions were the free troposphere size distributions measured during December 1989 (ALIVE III) and June 1990 (ALIVE IV), which resemble Junge's power-la w distribution. Each of the averaged aerosol size distributions was ap proximated by the sum of two log-normal distributions. Different chara cteristics of aerosol size distribution were observed between the two summer measurements of 1989 and 1990. Back-trajectory analysis reveale d that decreased aerosol concentrations were observed during June 1990 when the air mass was transported from the southwestern U.S.A.