The main submicron mass mode of atmospheric aerosols: Evolution and relation to clouds. A case study

Abstract

Atmospheric aerosol was investigated at Kleiner Feldberg Mountain in Germany by cascade impactors. Two identical impactors were operated side by side. One instrument collected the aerosol under ambient relative humidities (90% to 100%), the other sampled a gently dried aerosol at relative humidities around 70%. The instruments were also operated in clouds. Thirty-six runs were performed from the end of October to mid of November 1990. The mass distributions of these aerosols are bimodal with a coarse mode and a submicron mode in the accumulation range This main submicron mass (MSM) mode exhibits remarkable properties; (1) The MSM mode - and probably only this part of the submicron aerosol - is scavenged into cloud droplets. (2) Its evolution correlates with local SO 2 concentrations. (3) The modal masses vary, as do the modal diameters, but both parameters are stochastically related by a third-power regression. (4) The geometric standard deviations of the mode scatter within narrow limits. (5) The modal number concentrations do not correlate with the modal mass. (6) These number concentrations follow the cloud droplet concentrations, for the few events during the experiment.