The Size Distribution of Submicrometer Particles within and about Stratocumulus Cloud Droplets on Mt. Areskutan, Sweden

Heintzenberg, J., Ogren, J.A., Noone, K.J. and Gfirdneus, L., 1989. The size distribution of submicrometer particles within and about stratocumulus cloud droplets on Mt. Areskutan, Sweden. Atmos. Res., 24: 89-101. Stratocumulus clouds were studied at a sampling site on Mt. Areskutan, Sweden. Droplets were sampled with a counterflow virtual impactor (CVI), which extracted them from the cloudy air and evaporated them in a flow of warm, dry, filtered air. By analysing the evaporated droplets with an optical particle counter (OPC) size distributions of cloud condensation nuclei were determined in situ down to 0.04 mu m radius. The minimum radius of droplets sampled in the CVI was varied within the interval 4-11 mu m. With the same OPC, the size distribution of particles in interstitial and clear air before and after cloud passages were determined. On the average 80% of the fine particulate mass was incorporated in cloud droplets. The mass median radii of droplet residues increased by a factor of three with a droplet size increase from 4 to 11 mu m. An increase in the concentration of material in the droplets with droplet radius was observed. This increase by a factor of three over the range of 4-11 mu m droplet radius is in good agreement with previous independent results from the same study (Ogren et al., 1989). The results from the two studies support the hypothesis that condensational growth controls the concentrations of nonvolatile material in the cloud droplets near cloud base.