Weather system scale variation in radon-222 concentration of indoor air

Radon-222 concentration measurements using the charcoal adsorption technique were made continuously over periods of up to 2 years in three houses, two rural and one urban. The measurement records for all houses show a variation in radon concentration on a seasonal scale on which is superimposed shorter periods of relatively large magnitude fluctuations on a scale longer than the typically 4 5-day measurement duration. Regression analysis using meteorological data from a weather station remote from the houses shows that much of the variation in both monthly and 3-day mean radon concentration can be explained by regional scale external temperature variation. Wind speed, rainfall and barometric pressure apparently influence the 3-day values to a much smaller degree. Differences in the radon levels between the houses reflect the different geological radon potential of the two areas, with notably higher levels over limestone than glacial till and sandstone. Other differences within and between houses reflect house construction and occupancy factors.