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Original Research Papers

Test of a northwards-decreasing 222Rn source term by comparison of modelled and observed atmospheric 222Rn concentrations

Authors:

Lynette B. Robertson ,

School of GeoSciences, University of Edinburgh, GB
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David S. Stevenson,

School of GeoSciences, University of Edinburgh, GB
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Franz Conen

Environmental Geosciences, University of Basel, CH
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Abstract

Model-predicted atmospheric concentrations of 222Rn based on two different 222Rn source terms have been compared with observations in the lower troposphere. One simulation used a globally uniform 222Rn source term from ice-free land surfaces of 1 atom cm−2 s−1; the other assumed a northwards-decreasing source term (linear decrease from 1 atom cm−2 s−1 at 30°N to 0.2 atom cm−2 s−1at 70°N). Zero emissions were assigned to oceans. The northwards-decreasing source term improved predictions at four out of six stations north of 50°N, reducing the mean prediction/observation ratio from 2.8 to 0.87. In the latitudinal band between 30°N and 50°N, the northwards-decreasing source term resulted in systematic under-prediction of atmospheric 222Rn, whereas the uniform source term provided predictions close to observations. Predictions based on the northwards-decreasing source term were significantly (p < 0.01) better than those based on the uniform source term for an averaged vertical 222Rn profile around 44°N, but were not for one around 38°N. The results indicate that a northwards-decreasing source term could be a more realistic representation of actual 222Rn emissions than a uniform 1 atom cm−2 s−1 source term. However, the decrease in 222Rn source strength with increasing latitude might not begin at 30°N but somewhat further north. This hypothesis should be investigated through model-independent means.

How to Cite: Robertson, L.B., Stevenson, D.S. and Conen, F., 2005. Test of a northwards-decreasing 222Rn source term by comparison of modelled and observed atmospheric 222Rn concentrations. Tellus B: Chemical and Physical Meteorology, 57(2), pp.116–123. DOI: http://doi.org/10.3402/tellusb.v57i2.16781
  Published on 01 Jan 2005
 Accepted on 25 Oct 2004            Submitted on 26 Mar 2004

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