cannot select one of these approaches and say that that is the right way to do it. approach have to be taken, and maybe others in addition. samplers. At least these two types of This suggests that probably we need two types of These seem to be exemplified by essentially the mechanical type which does not collect everything, but only particles, presumably all the particles, you hope; perhaps you have not such precise volume control. On the other hand, the cryogenic type of sampler uses absorption or straight condensation freezing, attempting to get everything. The mechanical method lends itself to very large volume sweeping; the cryogenic system is essentially mass-limited. The mechanical system could be developed in such a way as to give considerable certainty concerning some constituents. Thecryogenic system enables you to find out practically anything you want to know about the constituents of the air. the technology discussion that we just heard. These are my impressions about the scientific implications of I don't feel that the contradictions that have been brought out are really contradictions, and we must move forward, not perhaps with all approaches, but certainly with at least dual approaches. To summarize, I say the mechanical sampler gives very large volumes, relatively low pre- cision of sampling, considerable economy in sampling, but the information content may be limited. The cryogenic sampler will tend to give a lower volume sample, with very high precision; the economy will not be so good, and it may be more expensive to do this, but you will get large information content. Another area of scientific implication which we probably should consider is that of the implications of the information that we get about the vertical pattern of distribution and the kinematics and dynamics of motion that go with this. After all, if all these different methods gave us the same answer as to what the dose to people would be or distribution on the ground or lower atmosphere, we really wouldn't care too much from the aerospace nuclear safety standpoint which of these various methods turned out to be right. Before we had the fallout problem, if you had asked the meteorologist what would happen in the stratosphere and troposphere or in the atmosphere generally, he would say that probably there would be different mixing rates in the troposphere and stratosphere--in the troposphere relatively fast and in the stratosphere relatively slow. As soon as we had the stratospheric fallout problem, a model was immediately proposed which had two regions, both of them rapidly mixing internally, but with a slow transfer from one to the other. Immediately another model was proposed, one in which there was slow transfer by mixing in the stratosphere but with a systematic circulation. different implications. These had One said there is uniform fallout from the stratosphere with time and location; the other said there is no uniform fallout with location, and essentially the circulation is a seasonal one. These impli- cations even had political importance, and these arguments about the circulation of the atmosphere were brought out in congressional hearings. above this. Now we have at least a third layer to look at, the mesosphere and what goes on We heard of one model which is based on sedimentation and essentially molecular diffusion. model indicates that the higher up you inject the material, the longer it takes to get to the ground. This This goes on indefinitely, although it happens fairly fast above a certain altitude, so it doesn't make much difference any more. If we put another layer on top of the stratosphere and add this too, we say the mesosphere on up is well mixed horizontally and vertically; we can say that we might actually have exponential feeding from the mesosphere into the next layer down. Then it gets involved with these other possible mechanisms, so we could have an exponen- tial rate of some fixed residence time, essentially a residence time concept which is converted into seasonal pulses by circulation of the stratosphere. Then you would have implications with respect to time, or, within the stratosphere, you might have increasing residence time essentially, or transient times with altitude, and when you get to the mesosphere that should put a limit--that means your residence time is limited by the maximum residence time of the stratosphere. 166 It has not been brought out in the meeting, except in attempts to interpret