0018933 in the atmosphere will alter the falling rates of the particles. Corrections for these effects can be made when adequate meteorological data is available. The local fallout as defined here will be down in 4.5 days or less, leaving aloft an aggregate of particles ranging from about 25micron diameter down to submicron size. For small shots the majority of this will be in the troposphere but for megaton-range yields a large propor- tion will be deposited in the stratosphere, Hence, in discussing world - wide fallout, it is desirable to consider it as subdivided into two classes identified as tropospheric, or intermediate, fallout and stratospheric, or delayed, fallout (Reference 23). The material left in the troposphere is thought to remain aloft up to forty days and to circle the earth a few times before reaching level. ground It deposits in relatively narrow bands, centered on the detonation latitude, with little evidence of diffusion across the stable air barrier located in the troposphere north of the equator. It is probably brought down largely by the scavenging effect of rainfall or other precipitation (Reference 23). Those particles which do not fall out within the first few weeks will remain suspended in the atmosphere for a prolonged period — a matter of around seven years on the average. This material originates exclusiveSAN BRUNO FRE 22 22