An account is given of about 250 impactions made on ten flights to sample chloride particles. The particles are captured on small perspex slides coated with a gelatin-silver nitrate solution and become manifest as circular discs. The calibration of the method is described and the lower limit of detection is found to be about 10−13 gm. NaCl.

The results show that, in the main, chloride particles originate from the sea surface but there is a possibility that the land or the coast produce some in the range 10−11 to 10−13 g. Particle concentrations are found up to about 2,000 litre−1 and total chloride contents up to 230 μg m−3. The variations of these particle concentrations with height, wind speed, state of sea and the three-day history of the sampled air are discussed.

Data are also presented on the concentrations of dust particles which were inadvertently sampled simultaneously with the chloride particles.