The monthly variations in plutonium air concentrations in Figure 1 and plutonium deposition in Figure 2 are very similar. The total plutonium- 239,240 deposited on the ground from all atmospheric tests to date is about 2.2 nCi/m? for the area near Argonne (Hardy et al., 1973). Therefore, the plutonium-239,240 added to what was already on the ground was 0.2% in 1973, 1.2% in 1974, 0.6% in 1975, 0.2% in 1976, and 0.5% in 1977. This information is useful to those individuals who are studying the dynamics of plutonium in lakes and oceans. In addition to plutonium, thorium and uranium concentrations in air have been determined for all three thorium isotopes and for total uranium at the three sampling locations. The uranium results are expressed as total uranium to allow comparison over the five-year period even though isotopic uranium results are available for the last two years. Results are similar at each location, and two of the distributions are presented here for illustrative purposes. Figure 3 is for thorium-232 and Figure 4 is for uranium at the same location. When the concentrations are expressed in units of aCi/m? for the five-year time period, the uranium and thorium are similar but do not show the same type of distribution as the plutonium, with its characteristic maximum in spring attributed to fallout. If the thorium and uranium concentrations are recalculated in terms of activity per gram of material collected on the paper, a lognormal plot of this data results in a straight-line fit. These are illustrated in Figure 5 for thorium-232 and Figure 6 for uranium. This implies a single source of particulate matter in air. A lognormal plot of the plutonium in air concentrations also results in a straight-line best fit, but the source of the plutonium is different. In addition, the specific activity of the material in air for thorium and uranium is related to the specific activity of thorium and uranium in soil. It appears that the amounts of thorium and uranium in an air sample are proportional to the mass of material collected on the filter paper, and the bulk of these elements in the air is due to resuspended soil. Accepting this premise, the relative amount of plutonium in air as a result of resuspended soil can be calculated. With the presently deposited plutonium in soil at 2.2 nCi/m?, the measured surface plutonium-239,240 concentration is about 25 fCi/g. Knowing the weight of residue material in each sample, the contribution from plutonium in soil can be determined. For example, in Figure 1, the 1976 plutonium-239,240 in air due to soil ranged from 6% in August to 22% in November of the total plutonium in the samples. The relative amount depends on the contribution from stratospheric fallout and mass of material. Resuspension factors (RF) for thorium-228, thorium-230, thorium-232, uranium, and plutonium-239,240 were calculated and are presented in Table 1. The thorium and uranium air concentrations are the five-year averages of those displayed earlier. The plutonium-239,240 is the five-year average concentration of the plutonium in air due to resuspended soil calculated with the above procedure. All measurements are from the same air sampling location. The amount of each nuclide in terms of ground deposition was obtained by a radiochemical determination of each 727