Spectral, broadband and personal solar UV measurements at a sub-tropical latitude

Abstract

An understanding of the solar terrestrial UV environment is necessary for the minimisation of solar UV exposures to humans and reduction of the risk of human sun-related disorders. In the Centre for Astronomy and Atmospheric Research at the University of Southern Queensland (USQ), Toowoomba, a research focus has been established to provide quantitative data on the solar UV environment and UV exposures to humans. As part of this research, spectral, broadband and personal UV measurements are employed. The ambient UVA and the erythemal UV is monitored continuously in 15 minute intervals with outdoor, calibrated, temperature stabilised meters. Anti-correlations have been measured between UV exposures and atmospheric ozone variations due to natural atmospheric processes. Increases of up to 14% over 5 days in the daily UV exposures to a horizontal plane were recorded. Personal UV exposures to humans are measured with polysulphone UV dosimeters. These dosimeters are fabricated from polysulphone in thin film form that is cast at the USQ. Quality assurance procedures are in place to produce film of reproducible and constant thickness, as changes in the film thickness can cause errors of up to 37% in the dose response. The personal erythemal UV exposures in gum tree shade have been quantified with the dosimeters. When summed over the whole day for each day in summer, the exposures were in excess of the erythemal UV exposures for horizontal plane incidence in full sun for an entire summer in England. A calibrated UV spectroradiometer is employed to measure the UV spectral irradiances in one nanometre steps. The UV meters are calibrated seasonally and each batch of polysulphone film is calibrated to the spectroradiometer. The UV spectrum in gum tree shade was measured and the spectral shade ratio decreased with increasing wavelength for all of the trees. The tree shade is not as effective at providing protection at the shorter wavelengths where the erythema, actinic and DNA action spectra have a higher relative effectiveness. The differences between the spectral biologically effective solar UV irradiances on the sun-normal and horizontal orientations for relatively cloud-free days were measured. For these cloud-free days parts of the human body exposed in a sun-normal direction may receive up to 27% higher erythemal UV exposure compared with any measurements or predictions of the UV exposures to a horizontal plane.