230 FRIEDLANDER AND PASCERI range) fell on a straight line on semilog paper. At low magnifications (larger size range), the data followed a linear relation on log—log paper, at least through the most reliable data points. Analytical ex- pressions for X(r) were obtained from these figures. The expressions were differentiated and divided by —k,A7 to yield n(r). The deposition velocity k, had an awkward form but was approximated by two simple expressions of the type k,~ r? for the two size ranges examined. The final expressions for n(r) are given ig Table 1. Table 1— FORMULAS FOR ate OFRUNS10 AND 11 Run 11 +f ; -_F-o6 x. 10%. ewi25.4 pth 29° 22(0. 0035'< r < 0.019 yw) ee22 x20 pateT, sale ca . LS tag 2 i 3 ow ; “Se 5. a _ WEee Swit the vertical barsFapgesenting: 55 ments. The orfohaiddiethe coritamination.on the grids used ferruns 10 and 11 was checked with blank,gridayIt was found that the partié tamination, level present before sampling_was, always less than:3%, of the total partfgle count madeat each magnification. ts ¥ 10 rT LOW MAGNIFICATION LOW MAGNIFICATION 2 n(r), PARTICLES/CM3- r— HIGH MAGNIFICATION — -— HIGH MAGNIFICATION 109 1078 | | | 107? tM 107! Fig. 5—Size distribution functions for runs 10 and 11. The number of particles in the vange between ry and r+ dy is given by n(r) dr. The distribution peaks near radii of 0.02 and 0.01 wu.