Variation of Natural Radon Flux Density Variation of Natural Radon Flux Density Over the Earth’s Surface: a 2010 UpdateOver the Earth’s Surface: a 2010 Update

Stephen ScheryStephen ScheryNASA/AMES, USANASA/AMES, USANew Mexico TechNew Mexico Tech

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What is meant by the phrase “natural What is meant by the phrase “natural radon flux density from the earth’s radon flux density from the earth’s surface”?surface”?

The amount of radon gas escaping to the The amount of radon gas escaping to the atmosphere from the earth’s surface per unit atmosphere from the earth’s surface per unit area per unit time under natural conditions, area per unit time under natural conditions, commonly measured in units of mBq mcommonly measured in units of mBq m-2-2 s s-1-1 or atoms cm or atoms cm-2-2 s s-1-1 . .

(21 mBq m(21 mBq m-2-2 s s-1-1 = 1.0 atoms cm = 1.0 atoms cm-2-2 s s-1-1 ) )

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What value are studies of natural radon What value are studies of natural radon flux density over the earth’s surface?flux density over the earth’s surface?

Required for precise tests with radon gas of Required for precise tests with radon gas of atmospheric transport models used to study atmospheric transport models used to study atmospheric pollution and global climate change.atmospheric pollution and global climate change.

Improve our basic science understanding of Improve our basic science understanding of radon and its transport at the earth’s surface radon and its transport at the earth’s surface useful for other applications such as indoor radon useful for other applications such as indoor radon pollution, atmospheric electricity, earthquake pollution, atmospheric electricity, earthquake prediction, and estimating fluxes of greenhouse prediction, and estimating fluxes of greenhouse gases.gases.

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Is there any relation between natural Is there any relation between natural radon flux density maps and maps of radon flux density maps and maps of “radon risk” and “radon source potential” “radon risk” and “radon source potential” used for indoor radon health concerns?used for indoor radon health concerns?

■ ■ Yes, but it is indirectYes, but it is indirect as discussed in the as discussed in the next three slides.next three slides.

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Natural radon flux density is strongly dependent on radium in the Natural radon flux density is strongly dependent on radium in the soil and its diffusion to the atmosphere driven by radon soil and its diffusion to the atmosphere driven by radon concentration gradients.concentration gradients.

Radon risk maps are also strongly dependent on radium in the soil, Radon risk maps are also strongly dependent on radium in the soil, but then other factors may become more important than diffusive but then other factors may become more important than diffusive transport: advective transport (driven by pressure gradients), transport: advective transport (driven by pressure gradients), construction factors of housing, living patterns of inhabitants, etc.construction factors of housing, living patterns of inhabitants, etc.

(continued)(continued)

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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 the Natural radon flux density is strongly dependent on the following combination of parameters following combination of parameters ФФDD1/21/2

where where ФФ is radon atoms per unit volume escaping to the soil is radon atoms per unit volume escaping to the soil pore space and D is the gaseous diffusion constant for pore space and D is the gaseous diffusion constant for radon.radon.

Radon source potential soil maps used for prediction of high Radon source potential soil maps used for prediction of high indoor radon risk are also strongly dependent on indoor radon risk are also strongly dependent on ФФ but then but then the following combination of parameters is often more the following combination of parameters is often more importantimportant

ФФk,k, where k is permeability of soil to air flow under an applied where k is permeability of soil to air flow under an applied

pressure drop. pressure drop. (continued)(continued)

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Comparison of a Natural Flux Density Map and a Radon Risk Map

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Review of Earlier Work: The Situation as of the mid 1990s

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Example of Older Radon Flux “Map” for the World

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An Early Attempt to Improve Sophistication of Flux Density Maps using Estimates from a Porous Media Soil Model Calibrated with Measurements of Flux Density

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Seasonal variations of radon flux density in South AmericaSeasonal variations of radon flux density in South America

January July

42.5 - 50 mBq m-2 s-1

35 - 42.527.5 - 3520 - 27.512.5 - 20

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More Recent Developments

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What are the Current Challenges?

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Independently Produced Maps do not agree well enough!

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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

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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”

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THANK YOU