Particles in the Lower Troposphere over the High Plains of the United States. Part I: Size Distributions, Elemental Compositions 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 United States. Two main particle modes are apparent: an accumulation mode between particle diameters (Dp) of 0.1?1 ?m and a coarse particle mode between Dp = 10?20 ?m. Near urban/industrial sources, a weak nucleation mode was detected at Dp < 0.1 ?m. 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 convecetive-scale processes. Large NaCl particles occasionally reached deep into the interior of the High Plains. The presence of relatively high concentrations of panicles with Dp ? 10 ?m has important implications for precipitation processes.