The data for all four locations show generally the same concentration levels at any given time and all siov' a gradual ani substantial increase during 1°Sh, The concentrations observed at Kodiak, Alaska durin, and follewine the Svoring:1952 tests are strikinely lov tr comparison with the 195h and 1955 concentration lata. The overage Sr? activity in 106 cubic feet of surface air ar veers te have increased from e pre-ivy test level of al out k dom to a preOestle level of some 0 dom and 2 post-Castle level of scme 200 dom, Comoarisen of the Sr?0 eir concentraticn data with the deily tote) fission product deta activity data obtained br the RRL group indicates "anpnarant" eges for the mixed fission products of from one month to several years with wide variations during any given month, . No conclusions with respect tr the sro production date mar be drawn from such data for a numer of reasons. The size distribution of the original bomb debris is devendent on the energy yield, orientation and environment of the weapon and for each case the mean size of particulates carrying Sr70 is expected to ve smaller than that of mixed fission products, Furthermore, the varticulates may be further frac- tionated by the action of rains, depending on the efficiency of scavenging by rains as a function of particle size. Another complication is that i:npcsed by the size-collection efficiency of the device itself, Additional diffi- culties are imnosed by the close snecing of tests during the lest several years, Finally, there are large day to dav variations in surface concertra- tion of Sr?0 and other fission products, acparentlv due to scavensing of surface air by vegetation and to the time interval -etween.rains, NYOO In spite of the many complicatins factors indicated above which limit tae meanin fulness of any individual measurement of Sr?0 concentration and its relation to total fission product activity or to other individval fission product concentration, the general reatures of the Sr90 surface air concentration data shed considerable light on atmospheric circulation and storage 5f