Mapping the Proportion of the Housing Stock Exceeding a Radon Reference Level

In order to identify homes with high radon levels as efficiently as possible, it is necessary to have accurate numerical information on radon-prone areas. Maps based on geological indicators are generally qualitative and sometimes contain significant errors. Maps based on radon measurement in homes are definitive if sufficient results are available. Often there are small numbers of measurements, making it difficult to map the fraction of the housing stock which exceeds the reference level. However, distributions of radon levels are usually lognormal, so modelling of the distribution allows the fraction of the housing stock exceeding any level to be calculated. A database of 62,555 radon results in southwest England is used to show that the data within 5 km grid squares are consistent with lognormal distributions and to develop techniques for estimating for fraction of homes exceeding a radon reference level in each grid square, even where data are sparse.