Temporal variation of radon levels in houses and implications for radon measurement strategies.

The results of continuous measurements of radon and other parameters in four buildings have been used to investigate the causes of temporal variations in radon concentration, and to assess and quantify the accuracy of different radon measurement strategies using passive detectors. The analysis showed that the four different houses had very different responses to outdoor temperature, wind speed and direction. As expected, the results from all four houses show that longer measurements allow the annual average radon level to be estimated more accurately than short measurements. In one house, which was shown to respond to the weather in a manner typical of many Northern European houses, 90 day etched track or electret measurements could provide estimates of the annual average concentration that were always within a factor of 1.5 of the true value, whereas estimates based on charcoal detectors could exceed a factor of 2 from the true value. The effect of applying seasonal correction factors was also investigated. In the typical house, applying these factors improved the accuracy of estimates of annual average radon concentration, whichever measurement technique was used. In the three less typical houses, where radon levels were influenced by wind speed and direction, the use of seasonal correction factors did not appear to be appropriate.