Soil CO2 flux measurements in volcanic and geothermal areas

The following topics are discussed: measurement of the radon-222 flux to the atmosphere; measurement of the lead-210 atmospheric flux; and the mean residence time of aerosols. A total global model is proposed for radon-222 and its daughters.

Geochemistry of Atmospheric Radon and Radon Products

Radon generated within the upper few meters of the Earth's crust by the radioactive decay of radium can migrate during its brief lifetime from soil into the atmosphere. This phenomenon leads to a human health concern as inhalation of the short-lived decay products of radon causes irradiation of cells lining the respiratory tract. This paper reviews the factors that control the rate at which two radon isotopes, 222Rn and 220Rn, enter outdoor and indoor air from soil. The radium content of surface soils in the United States is usually in the range 10–100 Bq kg−1. The emanation coefficient, which refers to the fraction of radon generated in a material that enters the pore fluids, varies over a wide range with a typical value being 0.2. Radon in soil pores may be partitioned among three states: in the pore air, dissolved in the pore water, and sorbed to the soil grains. Except in the immediate vicinity of buildings, radon migrates through soil pores principally by molecular diffusion. Average reported flux densities from undisturbed soil into the atmosphere are 0.015–0.048 Bq m−2 s−1 for 222Rn and 1.6–1.7 Bq m−2 s−1 for 220Rn. Soil is the dominant source of radon in most buildings. Advective flow of soil gas across substructure penetrations is a key element in the transport process. The advective flow is driven by the weather (wind and indoor-outdoor temperature differences) and by the operation of building systems, such as heating and air conditioning equipment. A typical radon entry rate into a single-family dwelling of 10–15 kBq h−1 can be accounted for by weather-induced pressure-driven flow through moderately to highly permeable soils. The extent to which diffusion through soil pores contributes to radon entry into buildings is not known, but in buildings with elevated concentrations, diffusion is believed to be less important than advection.

Radon transport from soil to air

Gas geochemistry and seismotectonics: a review

http://projects.itn.pt/Methasource_2015/Etiope_Martinelli_2002.pdf

Migration of carrier and trace gases in the geosphere: an overview

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.

Atmospheric pressure effects on 222Rn transport across the Earth-air interface

The flux of $sup 222$Rn 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$sup -2$ s$sup -1$ was obtained, compared with a range of values from 11 to 116 atoms m$sup -2$ s$sup -1$ calculated from near-surface $sup 222$Rn concentration profiles in seawater obtained by other investigators If these results are representative, the total oceanic contribution to $sup 222$Rn in the global atmosphere is only about 2% of all $sup 222$Rn 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

William E. Clements

Papers

Atmospheric pressure effects on 222Rn transport across the Earth-air interface

Radon 222 from the ocean surface