Development and characterisation of an ultra-long exposure UV dosimeter

Development and characterisation of an ultra-long exposure UV dosimeter

Excessive exposure to solar ultraviolet (UV) radiation is known to have detrimental effects on human health, some of which are cumulative in nature with impacts that may arise after years and decades of exposure. Therefore, it is important that the risk associated with prolonged UV exposure can be investigated; this requires long-term studies in which large-dose measurements can be accurately quantified.

Chemically-based UV dosimeters have been widely used to measure personal UV exposure since 1976. Despite the development of electronic UV dosimeters, chemical dosimeters maintain their suitability in human exposure research as versatile, labour- and cost-effective UV monitors that require no power. The main limitation of existing chemical dosimeters is their short dynamic measurement range, as they are saturated after relatively short exposure times. Consequently, prolonged personal UV exposures are estimated either from measurements spanning just a few days, with high uncertainty, or by the regular replacement of dosimeters on location, a practice that increases the cost and effort. A dosimeter that continuously measures longer periods would facilitate the task and provide more reliable estimates of prolonged UV exposures.

A new chemical UV dosimeter that meets this demand was developed and fully characterised in this study. The dosimeter, composed of unstabilised solvent cast polyvinyl chloride (PVC) in 16 μm thin film, is able to measure at least three weeks of full day exposure to solar UV radiation under clear sky conditions in summer at subtropical sites. This is twenty times the dose capacity of the most commonly used chemical UV dosimeter, a polysulphone based UV dosimeter.

The optimal parameters of the dosimeter’s construction and its dosimetric properties were experimentally investigated and characterised. The results show that the proposed dosimeter is easy to prepare, inexpensive, physically robust and easily analysed using an FTIR spectrometer. It responds mainly to UVB radiation, and hence can be calibrated for quantifying erythemally effective doses for long-term personal exposure studies. The response of the dosimeter to solar UV radiation is independent of temperature and dose rate. It also, exhibits an acceptable angular-error (defined as the deviation of the dosimeter’s relative response from the cosine function when the angle of incident beam is changed) and almost no dark reaction.

A field test was conducted to validate the proposed dosimeter with long-term personal UV exposure measurements. The erythemal UV exposures to selected anatomical sites on rotating head form manikins measured with the PVC dosimeter agreed well with the measurements obtained concurrently by a lower dose capacity chemical UV dosimeter, and are on a level with the results reported in earlier similar studies.

The characterised dosimeter is a valuable tool for research on the latent effects of cumulative UV exposure on human health. Measurements over longer periods will provide more reliable annual and lifetime exposure estimates as the larger the sample size (length of measurement period), the more accurately the sample will present the population (annual or lifetime UV exposure).