Measurements of the annual variation of the erythema dose of global radiation.

The share of erythema dose of global radiation (Der/G) shows significant diurnal and annual variations. This is the result of the dependence of the ratio Der/G on optical air mass. Maximum values of Der/G are found at times of low optical air mass, i.e., at noon and in summer, minimum values at sunrise and sunset hours as well as in winter. Another reason for the annual variation of the ratio Der/G is the changing amount of total atmospheric ozone. Therefore values of Der/G in fall are about 50% higher than in spring despite the same solar declination. Comparing measurements of erythema dose at two stations with different altitudes, a difference of 14% per 1,000 m is obtained.