SURFACE UVB IRRADIANCE MEASUREMENTS AT DURBAN DURING 1993

In a first-time field study, a Yankee Environmental Systems pyranomete r has been used to measure surface ultraviolet (UV) radiation at the U niversity of Natal, Durban. Integrated UVB (280-320 nm) and erythemall y active UV irradiance (280-330 nm), weighted by the Diffey action spe ctrum(1) for human erythema, were measured every five minutes for the period February to December 1993. Daily variation in erythemal irradia nce was compared with theoretical values generated by a surface irradi ance model (University of Natal, SPRI model), and good agreement obtai ned. integrated daily erythemal irradiances were investigated for the period of study and equivalent daily Minimal Erythemal Dose(1) (MED) u nits calculated Daily integrated erythemal irradiances of up to 7689 J m(-2), corresponding to a 36.6 MED equivalent, were recorded in Decem ber Monthly average UVB and erythemal UV irradiances for solar zenith angles (SZA) 25 degrees to 75 degrees were determined for February to December excluding July. Erythemal burn times(2) corresponding to thes e erythemal irradiances, for selected solar zenith angles, were calcul ated using an MED of 210 J m(-2). The seasonal variation of noon eryth emal burn times for Durban exhibited a minimum (9.6 minutes) and maxim um (44.5 minutes) during February to December and June, respectively.