CHAPTER 4 PHYSICAL MEASUREMENTS The aerosol and fallout sampling devices discussed in this chapter were placed in the field primarily to obtain representative samples of active airborne material for measurements of particle size and concen- tration, activities, and the physical and chemical nature of individual perticles, These objectives were only partially fulfilled. In this chapter, aerosols are taken as dispersions of solid or liquid particles in air which are so small that they readily follow the streamlines of air set in motion by air-suction devices of verious types, Fallout is that material which happens to deposit in or on various containers and surfaces. It is clear that the distinction is purely for instrumentel convenience and that no actual dividing line exists. 4ol PROPERTIES OF AEROSOLS Efforts were made to determine the properties of the ambient aerosols sampled at three island stations, William, Yoke, and Zebra, and on the Project 5A YAG's. belel Operatio Reco Many wmanticipated difficulties were experienced in the field. The wmexpected size of Shot 1 and the fire on Tare destroyed all but two of the air filter heads, greatly curtailing the filter eampling effort subsequent to Shot 1. The millipore filters from Shot 1, though torn or punctured, collected a considerable amount of activity and were useful for some purposes, After exposing electrostatic precipitators on 4sland stations for Shots 1, 2, and 3, with virtually no airborne activ- ity arriving within the preset 6~hr sampling period, the island stations were abandoned and one ESP was installed on each-of the Project 6.4 test ships, YAG 39 and YAG 40. The two salvaged air filter heads (DMT) were mounted on the flying bridge of YAG 40. Suecessful collections were obtained with these instruments from Shota 4 and 5, with the exception of the ESP on YAG 39, Shot 4. In this instance the plug to the aerosol inlet was inadvertently left in place during the sampling run. 82