The first observations of UV (290-400 nm) ever made at an agro-meteorological/radiometric station located in the metropolitan region of Maceio (9 degrees 28'S, 35 degrees 49'W, 127 m), Northeast Brazil, during 2008 are reported in this work. Solar UV radiation variability in different time scales and its fractional composition in the global solar radiation (G), that is, F-UV = UV/G is investigated under different sky conditions. The maximum daily UV solar irradiation (H-UV(d)) was 0.85 MJ m(-2) and the annual average 0.55 MJ m(-2). It was noticed that the largest contribution to the annual variation of the daily totals of UV are attributed to cloudiness than seasonality. Under partially cloudy sky, multi reflection was responsible for an increase of 11.1 and 18.8% in the UV levels, relatively to clear days. F-UV is inversely proportional to the global atmospheric transmittance (K-T): the daily percentage variation of F-UV was in the range of 2.33-2.95% in clear days and from 2.60 to 3.59% in cloudy days, with the annual daily average value of 2.8%. Linear empirical relations between the UV and G components for hourly and daily intervals under different K-T intervals were established and recommended, with the coefficient of determination (R-2) generally above 0.91. (C) 2012 Elsevier Ltd. All rights reserved.