Biologically effective dose of solar ultraviolet radiation estimated by spore dosimetry in Tokyo since 1980

The biologically effective dose of solar UV radiation has been measured in Tokyo since 1980 using Bacillus subtilis spores. To determine the cumulative dose in a half day, several samples of UV-sensitive spores were exposed in successive intervals from the solar-noon time. Because fluence-survival curves were exponential, the number of lethal hits received by the spores was calculated for each interval and termed inactivation dose (ID). The total number of hits obtained in a half day (half-day ID) was correlated with the amount of global insolation by a power-function regression. The regression analyses were performed for data collected on 35 days from 1980 to 1986 and for data collected on 53 days from 1989 to 1991. The latter data set yielded significantly larger estimates of half-day ID relative to the insolation than the former. (Author)