-6Air filter samplers have been used since long before the days of atomic energy, so that at the time when the difficult problem of sampling deposition arose, efficient collectors for airborne dust were already available. shows one of the Public Health Service units. Fig. 7 Such samplers have been an essential part of local industrial radiation protection programs. On the global] scale, airborne radioactivity has been of less direct concern as a possible hazard than has the entry of deposited radioactivity into the food supply. It has not been possible so far to relate the air concentrations to fallout in a simple, quantitative way. Air filter$sampies are unsurpassed, however, for providing concentrated samples on which counts can be taken quickly to give rapid early indications of the presence of fresh debris. The air concentrations also seem less sensitive to peculiarities of instrument exposure than is the fallout. Thus the patterns of variation in space and time obtained from the NRL 80th Meridian Network are qualitatively simple and interpretable. The NRL network is shown in Fig. 7 (Ref. 5). The monthly profiles of daily averageair activity plotted against latitude for the period July 1957- June 1958 show clearly the U.S. Plumbob Series, the USSR spring tests and _ Operation Hardtack. In the study of transport and deposition processes there is no doubt that the air concentration data are of fundamental quantitative importance. It is possible that they will be of more value in meteorological research than in evaluating hazards. The stratosphericsampling program will be of special interest to meteorologists. Because of very slow vertical mixing and the lack of efficient cleansing DOE ARCHIVI mechanisms such as precipitation, the stratosphere is a storage reservoir for finely divided radioactive debris injected into it. At first, attempts were g