Vertical distribution of atmospheric aerosol size distribution over south-central New Mexico

Abstract

The vertical distribution of background atmospheric aerosols was measured over south-central New Mexico as a part of the Atmospheric Lidar Verification Experiment (ALIVE) during four research field periods in the 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∼32 μm, using two Particle Measuring Systems (PMS) probes mounted on the wings of the NOAA King Air research aircraft. Vertical profiles of aerosol number concentrations of both fine- (0.1–2.0 μm) and coarse- (>2.0 μm) particle modes show seasonal differences, with higher number concentrations and higher mixed layer heights during summers. The measured aerosol size distribution data of each ALIVE intensive were averaged for boundary layer and free troposphere regions. These data mostly exhibit bi-modal distributions, 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-law distribution. Each of the averaged aerosol size distributions was approximated by the sum of log-normal distributions. Different characteristics of aerosol size distribution were observed between the two summer measurements of 1989 and 1990. Back-trajectory analysis revealed that decreased aerosol concentrations were observed during June 1990 when the air mass was transported from the southwestern U.S.A.