Variation of Natural Radon Flux Density
Over the Earth’s Surface: a 2010 Update
Stephen Schery
NASA/AMES, USA
New Mexico Tech
1
What is meant by the phrase “natural
radon flux density from the earth’s
surface”?
The amount of radon gas escaping to the
atmosphere from the earth’s surface per unit
area per unit time under natural conditions,
commonly measured in units of mBq m-2 s-1
or atoms cm-2 s-1 .
(21 mBq m-2 s-1 = 1.0 atoms cm-2 s-1 )
2
What value are studies of natural radon
flux density over the earth’s surface?
Required for precise tests with radon gas of
atmospheric transport models used to study
atmospheric pollution and global climate
change.
Improve our basic science understanding of
radon and its transport at the earth’s surface
useful for other applications such as indoor
radon pollution, atmospheric electricity,
earthquake prediction, and estimating fluxes of
greenhouse gases.
3
Is there any relation between natural
radon flux density maps and maps of
“radon risk” and “radon source potential”
used for indoor radon health concerns?
■ Yes, but it is indirect as discussed in the
next three slides.
4
Similarities and differences between natural
radon flux density and its mapping and maps
for radon risk or radon source potential
Natural radon flux density is strongly dependent on
radium in the soil and its diffusion to the atmosphere
driven by radon concentration gradients.
Radon risk maps are also strongly dependent on
radium in the soil, but then other factors may become
more important than diffusive transport: advective
transport (driven by pressure gradients), construction
factors of housing, living patterns of inhabitants, etc.
(continued)
5
Natural radon flux density is strongly dependent on the
following combination of parameters
ФD1/2
where Ф is radon atoms per unit volume escaping to the
soil pore space and D is the gaseous diffusion constant
for radon.
Radon source potential soil maps used for prediction of
high indoor radon risk are also strongly dependent on Ф
but then the following combination of parameters is often
more important
Фk,
where k is permeability of soil to air flow under an
applied pressure drop.
(continued)
6
Comparison of a Natural Flux Density Map and a Radon Risk Map
7
Review of Earlier Work:
The Situation as of the mid 1990s
8
Example of Older Radon Flux “Map” for the World
9
An Early Attempt to Improve Sophistication
of Flux Density Maps using Estimates from
a Porous Media Soil Model Calibrated with
Measurements of Flux Density
10
11
Seasonal variations of radon flux density in South America
January
July
42.5 - 50 mBq m-2 s-1
35 - 42.5
27.5 - 35
20 - 27.5
12.5 - 20
More Recent Developments
13
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What are the Current Challenges?
20
Independently Produced Maps do
not agree well enough!
21
22
Issues Needing Attention
■ Need a lot more, and better, radium and/or gamma
ray data, particularly for the southern hemisphere for
use as parameters in radon flux models.
■ Need more careful calibration and cross
comparisons of flux density measurements.
■ Need a research group with a mandate to work on
the global perspective not just local issues
■ Others
23
Where can I get more information?
■ Be on the look out for the upcoming
IAEA publication:
“The Proceedings of an IAEA/WMO
Technical Meeting, Vienna, 22-24 June
2009”
24
THANK YOU
25