particles. For the completely stagnant case, the time required for the profile to fall through this layer is, from equation (10), time to fall through stagnant layer r P, => 1 b |exp (2) - 1| - 4 [1 - exp (- 2) : (12) “b where p, is the density of the atmosphere at the top of the layer and Vy is the profile fall rate at the bottom of the layer. For the turbulent case, we assume a turbulent layer, of depth b, which is connected to stagnant atmosphere by discrete boundaries on both the top and bottom. Furthermore, the turbulence is assumed to be such that the impurity is completely mixed with the air in the layer so its concentration within the layer has the dependence - x Xx ). cc) exp (13) where A is the e-fold distance for air particles, x is the height of the bottom of the layer, and ch is the concentration of the impurity at x Since the layer is deep compared to the constant profile width of the impurity, most of the material will enter the layer before much leaves. Then the total amount of material in the layer, 7, at a given time, is xX,tb T -[ (* - *) Cy exp x b dx = Ae, a - exp (-2)] . (14) *b However, the rate of loss of the impurity is COME and must equal - de, —_—— - “by » which gives dt dD. _ [1 - exp(- b/A)] b Integrating gives c, b = c, (0) exp b (15) ¢- ——_—_——__:. , rd - expl- b/d) \ ‘b with ce,(0) being the concentration of the impurity at x at t= 0. Thus, it is seen from (15) that the time for c,, to decrease to 1/e - th of its original value is (A/vYE 1 - exp(- b/A}]. So, by comparing this value with equation (12), qualitatively speaking, the time required for the impurity to fall through the turbulent layer is approximately the same as for a stagnant layer. in summary, the authors feel the main value of the present work shows that diffusion has little effect on the vertical transport of particles of mass greater than 100 atomic units injected into the upper atmosphere. Furthermore, however crude our remarks have been concerning turbulence, we feel they will be of some value for future calculations concerning turbulence when more knowledge becomes available concerning the exact nature of turbulence in the upper atmosphere, 24