The spatial distribution of salt particles at cloud levels in Central Queensland

Large hygroscopic particles in the size range 0.5–200 μμg were collected on flights in central Queensland. The particles crystallized into distinct cubic shapes and were sized according to the volumes of these cubes. The concentrations so obtained showed only small variations in the vertical from 200 m to 1000 m and the shapes of the cumulative mass curves were similar to those measured near Hawaii. At cloud base levels (typically 1000 m), the concentrations decreased only slowly with distance inland–a penetration of 1100 km reduced the concentrations by a factor of five. It was found that the vertical and horizontal variations in the concentrations could be fitted to Tanaka's model quite well provided that the decrease associated with the pressure dependence on altitude was recognized. Preliminary chemical tests showed that the particles were mostly chloride with a small fraction of sulphate, and between 50 and 80 per cent contained some nitrate.