The impactors have been described in past AEC reports. 1, This discussion will involve only the filter samplers. Figure 2 shows the general configuration of two filter samplers developed at General Mills: (1) the Sub Micron Aerosol Collector (SMAC) unit developed for AFCRL, and (2) the Direct Flow Unit developed for the AEC. Both of these samplers utilize the same air mover, a single-stage Torrington blower powered by a half-horsepower Westinghouse aircraft 27 VDC motor, Both sample at about the same rate, drawing approxi- mately 500 cfm at 80, 000 feet and 300 cfm at 90, 000 feet. Both samplers have high efficiencies (virtually 100 percent) but they differ in the way that these efficiencies are achieved, The AFCRL unit uses a Delbag or Stanford Research Institute polystyrene fiber mat having 100 percent efficiency at all flow rates. Because of the large pressure drop of this type of filter, ten square feet are uti- lized in a cylindrical configuration. The AEC direct flow sampler utilizes the more porous IPC filter mat and achieves high efficiency by maintaining high linear velocities (above 500 ft/min) through one square foot of filter. with batteries weighs approximately 140 pounds. The direct flow system The AFCRL system is only a few pounds heavier. It should also be pointed out that isotopic analyses of filters obtained from the SMAC and Direct Flow samplers flown together on three comparison flights during 1960, indicated close agreement in terms of dpm per standard cubic foot of air sampled. 3 This agreement is, in part, attributed to the use of the PR-2 high altitude air flow meter developed for the Atomic Energy Commission andfirst put into use during late summer, 1960. is seven inches long and five inches in diameter. This unit shown in Figure 3 It is ordinarily mounted at the blower outlet and will measure flow rates in excess of 1000 cfm through an altitude range to 120,000 feet. Present accuracy is plus or minus 5 percent, In addition to the collection of particles, this laboratory has also been involved in work dealing with the collection of gases, H,0, CO,, Tritium, Carbon-14, and others. In recent years investigations have dealt with a method utilizing the ‘adsorption of these gases on crystalline zeolites, After extensive laboratory work an experimental gas sampler was designed and test flown on several balloon flights. early tests but gave doubtful results in later field trials at San Angelo, Texas . This unit performed well in Because of these results this laboratory received permission to perform a special test flight, conducted under the supervision of General Mills' personnel and utilizing this laboratory's facilities for preparation of the zeolite rather than having this done by an outside contractor. For comparative purposes two slightly different configurations were flown for sixty minutes at 72, 000 feet. These are shown in Figure 4. of the sampling units. Prior to collection the zeolite material is stored in sealed canisters at the top Upon reaching float altitude the motor blower is turned on for five minutes to clear en- trained water vapor and other gases from the system, At the end of this period the canister valves open, allow- the zeolite pellets to fall into frames between retaining screens, sixty minutes at a rate of approximately 220 cfm, Air is pulled through the adsorbing beds for PR-2 air flow meters monitor total flow and air is exhausted 151