of long lived fission products, The Sr79 air concentration history siovws a marked teneral increase following the Ivy ard Castle tests and thus appears to directly relate to the increased stratospheric storage followin~ there tests. g widely separated pe. The general equivalence of the concertrations observed for the four stations, n seorran.icel locatior, is strong indication that relatively old vebris rather than fresh fission rroduct activity is involved, Except for a few of the highest concentration values observed, the Sr?0 data do not reflect aiy considerable contribution from individual small wearons tests for which tronosvheric washout rates of severcl weeks or less have been estimated. An air filter device, horizontally oriented near the ground surface in zerearal will not collect large »articles which fall directly or particles tra ped in raindrons. Instead, it rill collict a vortion of tucse verticies woich mix domwarce between rains end nersist in surface air rlus sure of the perticles carried in the air dovmdraft assodated with rains for wiich the tr i] scavencing efficierc: of rains is lov, ‘Thus, the Sr? surface air concertre- tion data do not necessarily relate to the total denosition rate in ary direct mM2.NEF e The Sr?0 concentrations observed in surface air auring the Fall 195): and Sorinz 1905 are an order of magnitude lower than the limited U. 3. and British measurements of upper troposphere concentration during the same reriod, The numbers are not necessarily inconsistent when consideration is given to dilutio: oy cleaner surface air during dovmvard mixing, to reduction resultins from scavenpins by raivs, and to remcval fron surface air wy the filtration action ef vegetaion foliare and the action of fax enddev, The mean troposph«re NYOO concentration of Sr70 is undoubtedly a factor of 5 to 10 times higher than sucrace air values and thus corres onds to a total trovospneric air burden of ene megaton of fission or so. These considerations provide additional basis