Climatic and Seasonal Influences on Radon Time Series in an Environment of Low Anthropogenic Activity

Between June 2003 and March 2008 (1766 days), radon concentration and ambient temperature were monitored at hourly intervals in an environmentally-stable, rarely-visited partially-subterranean store-room in a public-service building. Sampling periods totalled 1025 days, the longest continuous sampling period and interval between sampling periods being 335 and 271 days respectively. Mean daily, monthly (calendar) and annual concentrations and temperatures were derived. For each calendar month, averages over corresponding months of at least three separate years were available. Similar means were generated from meteorological data collected 10 km from the measurement site. The mean and standard deviation over the whole radon data-set are 73.0 Bq.m and 62.7 Bq.m respectively, corresponding mean and SD internal temperatures being 26.2 C and 1.7 C, respectively. Radon concentration shows minimal or zero correlation with the three temperature parameters, atmospheric pressure and wind-speed, limited (negative) correlation with rainfall and possible (negative) correlation with relative humidity. Although statistically-derived Seasonal Correction Factors (SCFs) are conventionally used to convert radon concentration over a sub-year period to a notional annual mean, it is recognised in the literature that this approach is not without its problems, particularly where short-term measurements are concerned. A recent proposal uses external temperature to derive a local SCF, assuming positive temperature-difference between a building interior and its environment. To test this, surrogate SCF sets were derived using monthly mean radon concentration, external temperature and internal-external temperature-difference, and correlated with each other, and with the United Kingdom (UK) 1-month SCF set to quantify goodness-of-fit. Relatively good correlation (|r| = 0.59) exists between radon seasonality and the internal-external temperature difference, but poorer correlation (|r| = 0.18) with absolute external temperature, as implied by use of the temperature-based formula.