-llBoth carbon-14 and tritium (Bn?) occur naturally, are also produced in weapons tests, and are radioisotopes of elements which are of importance in meteorology and ecology. Thus the global transport cycles of bomb-produced carbon-14 and tritium are inextricably associated with the carbon dioxide and water cycles in nature (Ref. 12, 13, 14, 15). It seems inescapable that these tracers should become important tools in certain branches of meteorology 4. Development of Sampling Devices Considerable trial-and-error experimentation has gone into the design of ground-level collecting devices for airborne particulates, precipitation and deposited dust. Each system in use has been subjected to more or less thoroug calibration tests, and various more sophisticated new approaches have been suggested. However, by and large it has seemed preferable to use the simplest methods available except for special research purposes. The upper-air sampling problem, however, has not been susceptible to such simple solutions. A substantial part of the cost of the stratospheric monitor ing program has gone into attempts to calibrate the Ash Can system and to develop better ones. The following requirements will show the nature of the difficulties. (1) The particles to be collected are believed to be mainly in the diameter range from .01 to .1 micron. (2) The minimum air volume containing sufficient radioactivity for analysis is of the order of 300 standard cubic feet, that is, about 3,000 cubic feet at an altitude of 50,000 ft and 20,000 cubic feet at 90,000 ft. It has been DOE ARCHIVES estimated that the total mass of dust collected is of the order of .001 to .1l microgram. [3