Radon flux from soils

[Field@amrf-po.pmeh.uiowa.edu]

          In response to D. Steva, there are likely numerous factors
          that affect radon emanation from soils.  Soil moisture,
          barometric pressure and temperature are the first three
          that come to mind.


          I do agree with Ernest on the impact of moisture. We are
          in our second year of performing  "state wide" outdoor radon
          monitoring.  Very preliminary findings do indicate that soil
          moisture is indeed a very important factor on radon
          emanation from soils.


          Radon release from soils is most likely optimal when the
          soil is moist. A radon atom that enters a water filled soil
          pore space has a good chance of ending its recoil in the
          water.  If the soil is "moist", the radon is transferred
          to the air in the larger pore spaces.  If the larger pore
          spaces are filled with water, little transport of the radon
          will occur.

          Temperature is probably of lessor importance.  However,
          researchers have noted a 55% increased radon exhalation
          rate for a soil sample when the soil temperature was
          increased from 5 to 50 degrees C. However, I would suggest
          this type of a temperature increase is not common in natural
          conditions.


          Barometric Pressure is also a factor in the radon flux from
          the soil surface.  See Clements and Wilkening (Journal of
          Geophysical Research, Vol. 79, 1974; Schery et al., 
          Journal of Geophysical Research, Vol 87, 1982)


         There are also probably other factors such as soil type, etc.

          Regards, Bill 
          

          R. William Field, Ph.D.
          Department of Preventive Medicine 
            and Environmental Health
          University of Iowa
          Iowa City, Iowa 52242
          319-335-4413



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     I am no radon expert, but I would suspect that soil moisture has
     a big influence on radon emanation from soil.
     Dr. Tom Borak at Colorado State University may (should) be able
     to spread more light on this subject.

     Ernest


______________________________ Reply Separator _________________________________

Dear Radsafe:

Radon concentrations(and daughter concentrtions) in OUTDOOR air
fluctuate hourly, dialy etc. but most noticably from winter to
summer.  What factor (s) are primarily responsible for the
more significant seasonal fluctuations? From limited search of
literature - my first guess would be pressure differentials
(produced by temperature differences between soil and air)
pulling soil gas out of soil more in summer than winter?

Thanks

D. Steva