Effect of cloud on UVA and exposure to humans

The daily autumn and winter ultraviolet-A (320-400 nm) (UVA) exposures and 6 min UVA irradiance data for a southern hemisphere subtropical site (Toowo omba, Australia, 27.6 degreesS, 151.9 degreesE) are presented. This data is used to quantify the effect of cloud on UVA using an integrated sky camera and radiation system. Additionally, an estimate of the effect of enhanced UVA exposure on humans is made. The measurement system consisted of broad-b and visible-infrared and UVA sensors together with a sun tracking, wide-ang le video camera. The mean daily June exposure was found to be 409 kJ m(-2). Under the constraints of the uncertainty of both the UVA measurement syste m and clear-sky model, one case of enhanced UVA irradiance was found. Three cases of cloud enhancement of daily UVA exposure, approaching clear-sky le vels, were also determined using a calculated clear-sky envelope. It was al so determined that for a fulltime outdoor worker the additional UVA exposur e could approach approximately that of one third of a full winter's day. Fo r indoor workers with an outside lunch break of 12:00-1:00 P.M. the additio nal UVA exposure was on an average 6.9 kJ m (2) over three cloud-enhanced d ays. To the authors' knowledge this is the first paper to present some evid ence of cloud-enhanced UVA human exposure.