Radon-222 concentrations in a mountain canyon environment

Abstract

Measurements of222Rn concentrations near the mouth of a mountain canyon show diurnal changes consistent with the accepted model of canyon winds wherein surface air moving downslope at night accumulates radon, resulting in a steady increase in radon concentration and a decrease in air temperature. Maximum levels of approximately 0.5 picocurie/liter can occur. With the onset of up-canyon wind after surface heating in the morning, the radon level near the mouth of the canyon drops rapidly to nearly one tenth of the nocturnal maximum. The steady nighttime buildup can be interrupted by wind patterns that intercept the mountain at levels well below the mountaintop or by turbulent mixing induced by lee waves or other dynamic processes that increase temperature and decrease radon concentrations of the canyon air during the night. Measurements on a vertical section of the canyon near its mouth indicate high concentrations on the canyon floor under conditions of positive temperature lapse. Diurnal concentration patterns of radon at the top of the mountain ridge above the canyon show maxima in late moring and again in the early night hours.