Solar radiation characteristics, terms, definitions. Exposure measurements: principles and practices

Solar radiation is one of the the most important natural factor for its influence on environment and life.  If the UV solar spectrum is important in many biological processes it may be also very harmful if UV irradiance exceeds safe limits.  The UV radiation that reaches the ground depends on both geographical and astronomical parameters as well on the atmospheric conditions, often modulated by human activities influencing the air pollution and ozone layer; consequently the solar UV radiation is highly variable in space and time.  The relevant characteristics of solar radiation will be presented, and the most important parameters for its measurement will be described, including the used instrumentation, in particular wearable dosimeters required to determine the effective dose received by outdoor workers (e.g. film badges and programmable dosimeters).  In addition to direct measurement, estimation of solar radiation by means of predictive models is important. Another fundamental parameter is the UV index: this parameter is related to the well known erythemal effects of solar UV on human skin and it has been defined and standardised by several international institutions such as WMO, WHO, UNEP and ICNIRP. The relevance of these aspects will be presented and discussed.