Particles in the lower troposphere over the High Plains of the United States. Part I: size distributions, elemental composition and morphologies.

Abstract

Airborne measurements are presented of particle size distributions obtained during spring and summer at various locations in the High Plains of the US. Two main particle modes are apparent: an accumulation mode between particle diameters (Dp) of 0.1- 1 micrometer and a coarse particle mode between Dp=10-20 micrometer. Near urban/industrial sources, a weak nucleation mode was detected at Dp less than 0.1 micrometer. The accumulation mode was affected primarily by the type of airmass; recent involvement in precipitation was associated with significantly reduced particle concentrations in this mode. The coarse particle mode, which contained mostly local soil particles, was controlled primarily by mesoscale and convective-scale processes. Large NaCl particles occasionally reached deep into the interior of the High Plains. The presence of relatively high concentrations of particles with DP equal to or more than 10 micrometer has important implications for precipitation processes.-Authors