Measurement of Cloud Condensation Nuclei, Light Scattering Coefficient, Sodium-Containing Particles, and Aitken Nuclei in the Olympic Mountains of Washington

Abstract

Simultaneous measurements have been made of the concentrations of cloud condensation nuclei, sodium-containing particles, Aitken nuclei, and the magnitude of the light scattering coefficient of the air, for a period of two months in the Olympic Mountains of Washington State. Large short-term changes in the magnitudes of these four quantities were found to be related to variations in the local meteorological conditions. The most striking changes occurred with the build up and the evaporation of cumulus clouds upwind of the measuring site. The results indicate that growing clouds absorb (and also probably generate) large numbers of particulates, and that these particulates are released when the clouds dissipate. Precipitation also caused significant reductions in the concentrations of particulates in the air. Longer period variations in particulate concentrations were associated with the diurnal convective cycle and changes in air mass. Continental air contained higher concentrations of cloud condensation nuclei and Aitken nuclei than maritime air, but the Pacific Ocean appeared to be the principal source of sodium-containing particles. However, even in maritime air the measured concentrations of sodium-containing particles were always less than about 1% of the concentrations of cloud condensation nuclei active at 1% supersaturation.