The solubility of the atmospheric aerosol

The size distribution of the atmospheric aerosol was measured using three identical Climet counters at three relative humidities (RH), around 20%, ambient and near 100%. From the shift between particle size channels it was possible to determine the proportion of the aerosol which was water soluble. Measurements were made over a period of some months near Toronto. The number of occasions on which the droplet content of the ambient aerosol exceeded 20% was rather small. There were extensive periods when the droplet concentration was virtually zero (in spite of ambient RH between 60 and 70%) and changed very little when the RH was brought to near 100%. There were sudden changes from an aerosol which had only a low droplet content but was very soluble at near, 100% RH to one which was virtually insoluble even at saturation. An attempt was made to correlate the results with air mass origin by the use of five day back trajectories.