Source of origin of ice-forming aerosols as suggested by measurements on the soluble and non-soluble components of rain water

Samples of rain water have been collected on days of ice nuclei measurement, which have been associated concurrently with rain and categorised as high and low ice nuclei days. The soluble component in the rain water has been analysed for chloride, sulphate, sodium and calcium. The non-soluble component present has been estimated in terms of percentage reduction in transmittance of the rain water. Analysis of data has indicated that the chemical state of the air, in so far as its soluble component (hygroscopic part) is concerned, is not markedly different on the high and low ice nuclei days. The non-soluble component (non-hygroscopic part) is, however, consistently high on the high ice nuclei days. The findings point out that the natural ice nuclei are predominantly of land origin.