INTERNATIONAL SYMPOSIUM ON TRACE GASES AND RADIOACTIVITY ‘re I this is sufficient for Rn and 1 decay products, if 2, = 3 x 10° ‘ case. However, the concentratio n ved Rn™ decay products is still not this altitude. For this reason the is, in general, extended to the rekm <z < «© by putting K = 10° ———- 10° 10° a 2 10° x 10‘ cm?/see for z => 2,. We then z,) = —8,. Starting with an arbi- ‘alue, o(z,) = c, and the initial = —B,c, we computed the valu es 1) forjon — I, ++, 0, succes- undary condition at Z was then Itiplication with a suitable fact or. ating-point overflow—the g; inS z decreases—it was sufficie nt to ently small in most cases. The (Siemens model 2002) admits 10™ and 10" for variable point ‘o Include theless favorable cases z, instead of with Zn for which 5 } 10" a 10 D6 re 10 |: 20 aM 10 E oO 5 7 10 2 12 m 10 5 10° -l 10" a 100} a,8; > 100 1 iS suggested by the exponential] solutions (¢ a. 10°). In fact he boundary conditions atz = ‘o are negligible if p < n, © error caused by replacing the ‘tep function the computation ome cases with a larger number atlons were negligible. RESULTS AND CoMPARISO N XPERIMENTAL Data shows the Rn™ profiles whi ch th the typical K profiles giv en are standardized to a mea n 1 atom/cm! sec. Exhala tion everal places having nor mal he soil material indica te an rate of 0.2 to 1.5 ato ms/em? 1 rather good agreement with 1 atom/em? see which was ally by Israel [1958, 196 2] ransport of Rn™ in the sur Tound. It follows that the files in Figure 2 should be with the results of mea mental areas having normal 3803 \ Orem 10cm Im 10m 100m Tkm km 30km Altitude Kite. 2. Vertical profiles of radon (Rn**), calculated with Era = 1 Rn atom/cm® see for the K profiles JVWN, WNN, NWN, NNN, and SSN. Figure 2 indicates that the Rn*” concentration in the boundarylayer, being strongly dependent on the mixing rate, varies by about a factor of 100 from a minimum value of about 0.3 x 107° ¢/m* for strong turbulence (case SSN} to a maxi- mum value of about 30 x 10° c/m? for a strong inversion (case JIVN). This range corresponds rather well to the observed fluctuations of the concentration near ground level. Compared with this variation, the influence of short time changes of the Rn™ exhalation from the #round is negligible. The theory indicates that & mean concentration of about 10° ¢/m* should be. expected near ground level, in agreement with the mean values of most measurements at continental locations [Hultguist, 1956; Israel, 1962], Figure 2 also shows the interesting result tht variations of turbulence have only a little influence on the concentration in the region from 0.5 to 2 km, because in this region the ay are intersecting. For the rather extreme cases which we have discussed, the concentration in this region varies only by about a factor of 5 as compared with a factor of 100 in the air near the earth’s surface. The radioactive decay of Rn™ (t. = 3.8 d) leads to a monotonic decrease of the concentration with inereasing altitude. According to the theory, a significant concentration gradient should be expected only in the boundary laver and for very weak turbulence, ie., especially during strong inversion periods at night (case IWN in Figure 2). This theoretical conclusion can be checked by the observations of Moses et al. [1960]. Figure 3 shows observed Rn™ and temperature profiles at the end of nightly periods which had high stabilitv and rather constant wind velocity. The observed profiles during strong inversions correspond rather well to the calculated profile for this case (profile TWN). Beyond the ground laver over continental areas we made only a few series of Rn™ measurements which allow a comparison with the