In recent years, there has been too much concern regarding solar ultraviolet (UV) radiation received at the earth,s surface because of its biological hazards affecting living organisms. Although the geographical distribution of ground-based UV network is relatively good in some continents, over Asia and Africa, the number of UV instruments are not sufficient for research purposes.

Iran, as an Asian country, is also suffering from the lack of UV monitoring network with the exception of one ground-based UV site in Hamadan which was recently established for measuring the daily integrated UVB at the surface.

Using a radiative transfer model and various meteoroloical data (for 8 years) such as total column ozone, cloudiness, surface albedo, surface air pressure, relative humidity, visibility and daily total solar radiation (TSR), this paper determines the geographical distribution of annual integrated biological surface UV irradiances such as UVB, erythema, cataract and keratitis.

The comparison is made for cloud-free and all-sky conditions for eight selected cities distributed from the southern tip of the country (25 N-60 E) to the northern border (39 N-48 E). It is shown that the difference between the annual UV at south and north in all-sky condition is larger than the differences in cloud-free condition. The ratio of some biological UV irradiances at southern cities to the same component at northern cities shows a factor of two and more which is quite significant. The possible reasons for each case are discussed.