Measurements of radon exhalation from a gravely sandy loam have been made in a semi‐arid climate by using a combination of closed accumulation, flow‐through accumulation, and 222Rn and 210Pb soil profiles. The meteorological factors that most affected the instantaneous value of exhalation of 222Rn were atmospheric pressure and rain. Effects due to other parameters such as wind or temperature were either comparatively small or undetectable. No evidence was seen for migration of radon from distant (≫10m) sources or for an effect on exhalation due to limited nearby seismic activity. Measurements for 220Rn indicated its exhalation was also sensitive to pressure variation but to a lesser extent than for 222Rn. While instantaneous exhalation of 222Rn could easily vary by a factor of 2 or more, time‐averaged exhalation was found to be close to that expected for pure diffusion. There is thus some indication that the time‐averaged effect of cyclic environmental variables is small for this soil. Comparison with transport equations indicates that it is difficult to explain the observed variation in surface flux density solely in terms of the radon concentration gradient in the top few decimeters of soil. A contribution to transport from direct flow, perhaps through inhomogeneities such as cracks or channels, is one possible explanation.

The transport of 222Rn from fractured rock has been studied in an abandoned mine. Pressure‐induced flow (both natural and artificial) is quite important and can easily cause an order of magnitude increase in the instantaneous transport of radon into the tunnel airspace compared to that due to flowfree diffusion. Permeability studies indicate that large‐scale cracks of surface density of the order of several cracks per square meter dominate flow. In first order, effective flux due to natural pressure variation follows an approximate dP/dt dependence. In higher order, there exists an enhancement of time‐averaged flux by typically a factor of 2 due to natural pressure variation. Mathematical modeling indicates that the relation between pressure and the strength and time dependence of the radon transport is difficult to explain solely with conventional models for semi‐infinite homogeneous porous media. A model of cul‐de‐sac chambers is proposed to account for some of this dependence.

A continuous recording accumulator method has been employed to study the effect of natural pressure cycles such as due to the passage of cyclonic weather systems on the time‐averaged flux of 222Rn from the soil. Results indicate a modest net enhancement of flux (∼10%) for pressure variation with standard deviations on the order of 0.2 in Hg.

A two-filter, continuous monitor has been developed for atmospheric (222)Rn. Features include a sensitivity of better than 0.01 pCi/l, a high specificity for (222)Rn, and immediate start up capability. The monitor has been computer modeled to facilitate calibration and selection of operating parameters. The filters are stationary and require no moving parts for control. Field trials indicate high reliability and maintenance-free operation for periods of a week and longer.