The effect of large‐scale atmospheric pressure changes on the 222Rn flux across the soil‐air interface is investigated. Field data collected during 1972 and 1973 show that pressure changes of 1–2% associated with the passage of frontal systems produce changes in the 222Rn flux from 20 to 60%, depending upon the rate of change of pressure and its duration. A simple model of molecular diffusion combined with pressure‐induced transport in the soil has been confirmed by laboratory experiments using a vertical column of 226Ra‐bearing sand. On the basis of this model, pressure changes of 10–20 mbar occurring over a period of 1–2 days produce Darcy velocities of the order of 10−4 cm s−1 near the surface of a soil having a permeability of 10−8 cm2. The corresponding variations in the 222Rn flux predicted by the model are in agreement with those observed from valley alluvium in central New Mexico.

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 flux of "n from the ocean surface has been measured by the accumulation method off the windward coast of the island of Hawaii. A figure of 74 + 8 atoms m -2 s -x was obtained, compared with a range of values from 11 to 116 atoms m -"s -• calculated from near-surface "Rn concentration profiles in seawater obtained by other investigators. If these results are representative, the total oceanic contribution to "n in the global atmosphere is only about 2% of all 2:•2Rn exhaled from continents. Fluxes obtained by the accumulation method in shallow bay waters nearshore were intermediate between the very low value measured in the open ocean and the values obtained onshore. mospheric radon and continental dust near the Antarctic and their correlation with air mass trajectories computed from Nimbus 5 satellite photographs, J. Appl. Meteorol.,

Radon 222 concentrations in the air in Carlsbad Caverns have been measured at different times of year in order to define certain features of the natural circulation of the cave atmosphere and to estimate the internal radiation exposure to visitors and Park Service personnel. Concentrations average 48 pCi/l. in the summer when the temperature lapse rate provides a stable cave atmosphere. In the winter months air from outside having a "' Rn concentration of only about 0.2 pCi/l. mixes with the cave air reducing radon levels to about 15 pCi/l. A simple model obtained by equating the input of "' Rn atoms from the rocks and soils of the cave's interior surfaces to the sum of terms for radioactive decay and dilution of the cave atmosphere by outdoor air enables one to predict, for steady-state conditions, the approximate levels of activity to be expected for all months of the year. If it is assumed that the short-lived daughter products of 222Rn are present in equilibrium amounts, Park Service personnel spending most of their time underground approach the 4 WM/yr (working level months per year) exposure limit established tor the uranium industry. A visitor on a 3-hr trip through the Caverns would receive only a few per cent of the exposure guides for the general population.

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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.

Concentrations Of 222Rn, 210Pb, 210Bi, 210Po, and 90Sr were determined in surface air on the windward side of Hawaii. About three fourths of the 222Rn on the lower slopes of the island is due to emanation from the island surface, whereas the remainder of the 222Rn and most of its long‐lived radioactive daughters, 210Pb, 210Bi, and 210Po, are advected from distant continental sources. The transient time of air masses over the island, the transit time from distant continental regions, and the mean aerosol residence times above and below the trade wind inversion are estimated to be about 13 hours, 15–20 days, and 5 and 2 days, respectively.

Natural radioactivity in the atmosphere is used as a ``tracer'' in the study of aerosol particle-size distribution in the submicroscopic range. Particulate matter is collected by a device which first ionizes the particles and then separates them according to their mobilities. The results indicate that most of the natural radioactivity in the atmosphere attaches itself to particles having diameters in the range 0.001 to 0.04 micron. A predominant grouping of the activity occurs in the vicinity of two particle diameters: 0.009 and 0.018 micron. The relationship between the distribution of radioactivity and the abundance of particles in different size ranges is discussed.