This study reports the first observations of effective erythema radiation (EER) from an arid region of Iran. The hourly and daily measured clear-sky global solar radiation (G) and biologically important EER incident on a horizontal surface at Esfahan, Iran, during 2002–2004 are used. The EER irradiation was recorded by a spectrophotometer Brewer type MK IV mounted on the roof of the Esfahan site. The total daily broadband radiation was measured using an Eppley Pyranometer (Kipp & Zonen CM) at the same site. Using the mentioned experimental data, a linear relationship (EER = β × G + α) is established between daily integrated totals of EER and the daily totals of broadband global solar radiation (300–3000 nm). At statistically significant levels (p < 0.05 and R2 > 0.92) a good linear correlation between the daily G and EER was found. The observed (G) data is a routine meteorological measurement at many meteorological stations and such a relationship would enable estimates of the daily EER to be made from accessible records. The seasonal variability of EER/G is also discussed. The effect of the annual cycles of solar zenith angle (SZA) and total column ozone (TCO) on the ratios (EER/G) is presented and the correction factors are determined for the inclusion of the ozone cycle
