A general model to predict individual exposure to solar UV by using ambient irradiance data

A numerical model for quantifying exposure to natural and artificial light in human health research

Various skin and ocular pathologies can result from overexposure to ultraviolet radiation and blue light. Assessing the potential harm of exposure to these light sources requires quantifying the energy received to specific target tissue. Despite a well-established understanding of the light-disease relationship, the quantification of received energy in diverse lighting scenarios proves challenging due to the multitude of light sources and continuous variation in the orientation of receiving tissues (skin and eyes). This complexity makes the determination of health hazards associated with specific lighting conditions difficult. In this study, we present a solution to this challenge using a numerical approach. Through the implementation of algorithms applied to 3D geometries, we created and validated a numerical model that simulates skin and ocular exposure to both natural and artificial light sources. The resulting numerical model is a computational framework in which customizable exposure scenarios can be implemented. The ability to adapt simulations to different configurations for study makes this model a potential investigative method in human health research.

Health risks of extended exposure to low-level UV radiation - An analysis of ground-based and satellite-derived data

This study aims to indicate the importance of revising current health recommendations concerning the duration of exposure and individual sensitivity of the skin to solar ultraviolet (UV) radiation. For this purpose, a 16-year data series (2005-2020) of erythemal radiant exposure (H_er) and UV index (UVI) for Serbia was analyzed. The UV-related risk was estimated for lighter skin (skin phototypes I-IV) under prolonged exposure on days when maximum UVI was below the recommended protection threshold (UVI_low days, for UVI < 3). Risk assessment was performed for seasonal exposure using satellite-derived data (OMUVBd product) previously validated by ground-based measurements in Novi Sad. The assessment of harmful effects included an analysis of the relation between the daily maximum UVI and the corresponding daily H_er, the occurrence of UVI_low days, the exceedance of minimal erythema dose (MED), and the minimum duration of exposure to induce erythema (t_MED) for all lighter skin phototypes. It was found that the share of UVI_low days in the total number of days in Serbia increases with the latitude, with the highest percentage in winter (up to 69.454%) and the lowest in summer (up to 3.468%). The results show that the daily H_er frequently exceeded the harmful threshold for lighter skin phototypes I-IV (on average by 91.521, 84.923, 70.556, and 56.515%, respectively) on UVI_low days. It was found that prolonged exposure on days with a maximum of UVI = 2 poses a significant risk of erythema for all lighter skin phototypes, even for a duration of 3 h in the middle of the day, as well as medium risk for UVI = 1, and an absence of risk for UVI = 0. The results suggest that health recommendations should be revised, especially in the mid-latitudes, where the share of UVI_low days is large, and in areas where the population is predominantly lighter-skinned.

Bringing Light into Darkness-Comparison of Different Personal Dosimeters for Assessment of Solar Ultraviolet Exposure

(1) Measuring personal exposure to solar ultraviolet radiation (UVR) poses a major challenges for researchers. Often, the study design determines the measuring devices that can be used, be it the duration of measurements or size restrictions on different body parts. It is therefore of great importance that measuring devices produce comparable results despite technical differences and modes of operation. Particularly when measurement results from different studies dealing with personal UV exposure are to be compared with each other, the need for intercomparability and intercalibration factors between different measurement systems becomes significant. (2) Three commonly used dosimeter types—(polysulphone film (PSF), biological, and electronic dosimeters)—were selected to perform intercalibration measurements. They differ in measurement principle and sensitivity, measurement accuracy, and susceptibility to inaccuracies. The aim was to derive intercalibration factors for these dosimeter types. (3) While a calibration factor between PSF and electronic dosimeters of about 1.3 could be derived for direct irradiation of the dosimeters, this was not the case for larger angles of incidence of solar radiation with increasing fractions of diffuse irradiation. Electronic dosimeters show small standard deviation across all measurements. For biological dosimeters, no intercalibration factor could be found with respect to PSF and electronic dosimeters. In a use case, the relation between steady-state measurements and personal measurements was studied. On average, persons acquired only a small fraction of the ambient radiation.

Estimating personal solar ultraviolet radiation exposure through time spent outdoors, ambient levels and modelling approaches

BACKGROUND

 Evidence on validation of surrogates applied to evaluate the personal exposure levels of solar ultraviolet radiation (UVR) in epidemiological studies is scarce.

OBJECTIVES

 To determine and compare the validity of three approaches, including (i) ambient UVR levels, (ii) time spent outdoors, and (iii) a modelling approach integrating the aforementioned parameters, to estimate personal UVR exposure over a period of six months among indoor and outdoor workers and in different seasons (summer/winter).

METHODS

 This validation study was part of the EU ICEPURE project and was performed between July 2010 and January 2011 in a convenience sample of indoor and outdoor workers in Catalunya - Spain. We developed linear regression models to quantify the variation in the objectively measured personal UVR exposure that could be explained, separately, by the ambient UVR, time spent outdoors, and modelled UVR levels.

RESULTS

Our 39 participants - mostly male and with a median age of 35 years- presented a median daily objectively measured UVR of 0.37 standard erythemal doses (SEDs). The UVR dose was statistically significantly higher in summer and for outdoor workers. The modelled personal UVR exposure and self-reported time spent outdoors could reasonably predict the variation in the objectively measured personal UVR levels (R² = (0.75, 0.79)), whereas ambient UVR was a poor predictor (R² =0.21). No notable differences were found between seasons or occupation.

CONCLUSIONS

 Time outdoors and our modelling approach were reliable predictors and of value to be applied in epidemiological studies of the health effects of current exposure to UVR.

Personal Solar Ultraviolet Radiation Exposure of Farmworkers: Seasonal and Anatomical Differences Suggest Prevention Measures Are Required

INTRODUCTION

Farmworkers are at risk of excess exposure to solar ultraviolet radiation (UVR) during their work activities, especially if they work in geographical areas with high ambient solar UVR levels such as in South Africa. Excess exposure to solar UVR may lead to several negative health effects such as certain cataracts and skin cancer. This study evaluated personal solar UVR exposure of a group of farmworkers to determine if they were at risk of health-related problems due to excess solar UVR exposure.

METHODS

Polysulphone film (PSF) badges were placed on the shoulder, arm, and top of the head of outdoor and indoor farmworkers on a macadamia nut and avocado farm in the Limpopo province for the duration of their daily work shift to evaluate their total daily solar UVR exposure. Sixteen days were assessed for each of the three, high solar UVR seasons, i.e. autumn, spring, and summer.

RESULTS

During autumn, farmworkers' arms received the highest solar UVR exposures (geometric mean (GM) = 7.8 SED, where 1 standard erythemal dose (SED) = 100 J/m2, 95% CI 6.1-9.8 SED) while the highest exposures were on the top of the head during spring (GM = 11.6 SED, 95% CI 7.3-17.4 SED) and summer (GM = 13.9, 95% CI 10.4-17.9 SED). Statistically significant differences in solar UVR exposure were found between the body sites during spring and summer but not autumn.

CONCLUSIONS

The relatively high daily solar UVR exposure levels of farmworkers suggest this occupational group is at risk of excess solar UVR exposure and preventive measures with awareness information to safeguard health is necessary for employers and employees.

Possibilities to estimate the personal UV radiation exposure from ambient UV radiation measurements

People are exposed to solar ultraviolet radiation (UVR) throughout their entire lives. Exposure to UVR is vital but also poses serious risks. The quantification of human UVR exposure is a complex issue. Personal UVR exposure is related to ambient UVR as well as to a variety of factors such as the orientation of the exposed anatomical site with respect to the sun and the duration of exposure. This is mainly determined by personal behaviour. A variety of efforts have been made in the past to measure or model the personal UVR exposure of people and often personal UVR exposure has been expressed as the percentage of ambient UVR. On the other hand, ambient UVR is being monitored at a variety of places and measurements are available even online. This suggests that both the knowledge of personal UVR exposure and measurements of ambient UVR is required. In this paper, a summary on the different methods, which use ambient UVR measurements to estimate personal UVR exposure of people, as well as a few examples, are given. Advantages and disadvantages will be discussed as well as possibilities and limitations. This also includes an overview of appropriate terminology, units and basic statistic parameters to describe personal UVR exposure.

Developing a UV climatology for public health purposes using satellite data

The effects of solar ultraviolet (UV) radiation on life on Earth differ greatly. While overexposure to UV rays is harmful, small amounts of exposure are necessary for the synthesis of Vitamin D and good health. To optimize individual exposure to solar UV, it is therefore crucial to use UV data sources representative for entire populations and realistically accounting for various influencing factors. A UV climatology for Switzerland based on satellite data has been developed to provide risk estimates at population level. An algorithm generating ground-based radiation estimate has been transformed from the visible to the UV wavelength domain by adapting both a clear-sky radiation transfer model and a cloud modification factor model using satellite imagery. The algorithm allows the computation of global UV erythemal irradiance at a spatial resolution of 1.5 - 2 km and an hourly temporal resolution over fifteen years. A validation, conducted with measurements from three meteorological stations over ten years, showed that the expanded uncertainty for low hourly UVI values (UVI < 3) is about ± 0.3, while for high hourly UVI values (UVI > 6) it can go up to ± 1.5. In clear-sky situation, the uncertainty is in the range of 10-15%. The climatology developed allows to visualise potential UV exposure at regional and national scale. National prevention intervention could use new strategies to better focus on populations at risk and better tailor available researches. The UV climatology allows a high versatility in adapting the data extraction to the goal of studies using it. Further tailored data extraction and analysis will be necessary to exploit this climatology in a wide range of environmental and occupational health applications. Its development was focused on Switzerland, but the techniques used can be extended globally.

Estimation of Individual Exposure to Erythemal Weighted UVR by Multi-Sensor Measurements and Integral Calculation

Ultraviolet radiation (UVR) can be hazardous to humans, especially children, and is associated with sunburn, melanoma, and the risk of skin cancer. Understanding and estimating adults’ and children’s UVR exposure is critical to the design of effective interventions and the production of healthy UVR environments. Currently, there are limitations to the ways computer modeling and field measurements estimate individual UVR exposure in a given landscape. To address these limitations, this study developed an approach of integral calculation using six-directional (up, down, south, north, east, and west) field-measured UVR data and the estimated body exposure ratios (ER) for both children and adults. This approach showed high agreement when compared to a validated approach using ambient UVR and estimated ER data with a high r-square value (90.72% for child and adult models), and a low mean squared error (6.0% for child model and 5.1% for adult model) in an open area. This approach acting as a complementary tool between the climatology level and individual level can be used to estimate individual UVR exposure in a landscape with a complicated shady environment. In addition, measuring daily UVR data from six directions under open sky conditions confirmed that personal dosimeters underestimate actual individual UVR exposure.

Comparison of GOME-2 UVA Satellite Data to Ground-Based UVA Measurements in South Africa

Satellite estimates of surface ultraviolet A (UVA) (315-400 nm) from the Global Ozone Monitoring Experiment (GOME)-2 were compared to ground-based measurements at four stations in South Africa for 2015. The comparison of daily exposure and daily maximum irradiance was completed for all-sky and clear-sky conditions. There is a strong linear correlation between the satellite and ground-based data with a correlation coefficient (r) between 0.86 and 0.97 for all-sky conditions. However, at three of the stations the satellite data are underestimated compared to ground-based data with a mean bias error (MBE) between -8.7% and -20.6%. A seasonal analysis indicated that there is a link between the bias in ground-based and GOME-2 UVA and cloud fraction. Factors such as aerosols, surface albedo, altitude and data resolution may contribute to the underestimations found at the three sites. These results indicate that satellite estimates of surface UVA over South Africa do not exhibit the same behavior as other stations around the world and therefore require further validation.

Public Health Messages Associated with Low UV Index Values Need Reconsideration

Overexposure to ultraviolet (UV) radiation is the main modifiable risk factor for skin cancer. The Global Solar Ultraviolet Index (UVI) was introduced as a tool to visualize the intensity of UV radiation on a certain day, which should enable and encourage people to take appropriate protective measures. The ‘low’ exposure category of the UVI, defined by a rounded UVI value of 0, 1 or 2, was linked to the health message ‘No protection required’ by the World Health Organization and partner organizations. However, published evidence corroborating this advice is not available. To evaluate the erythemal risk of low UVI days, we analyzed 14,431 daily time series of ambient erythemal irradiance data measured at nine stations of the German solar UV monitoring network during the years 2007–2016. We analyzed the proportion of days in the sample for which ambient erythemal doses calculated for various time intervals exceed average minimal erythemal doses (MEDs) of the Fitzpatrick skin phototypes I–VI to assess the potential for erythema arising from sun exposure on days with low UVI values. Additionally, we calculated for each day the minimum exposure duration needed to receive one MED. Our results indicate that on days with a UVI value of 0, risk of erythema is indeed negligible. Conversely, the abovementioned health message appears misleading when melano-compromised individuals (skin type I and II) spend more than 1.5 hours outdoors on days with a UVI value of 2. Under rare circumstances of prolonged exposure, MEDs of the two most sensitive skin types can also be exceeded even on days with a UVI value of 1. Hence, current WHO guidance for sun protection on days with low UVI values needs reconsideration.

Erythemal UV Radiation on Days with Low UV Index Values-an Analysis of Data from the German Solar UV Monitoring Network over a Ten-year Period

According to the World Health Organization and partner organizations, no protection against ultraviolet (UV) radiation is required on days with "low" values (i.e., values <3) of the Global Solar Ultraviolet Index (UVI). Erythemal irradiance (E_er ) data of such days were analyzed to evaluate this claim. Measurements from 9 stations of the German solar UV monitoring network from 2007 to 2016 yielded 14,431 daily E_er time series of low UVI days. Erythemal doses for certain fixed time intervals-acquired from measurements on horizontal planes-were compared with the average minimal erythemal dose (MED) of skin phototype II. Doses from days with rounded UVI values of 0 were insufficient to induce erythema and even on days with rounded UVI values of 1 doses exceeding 1 MED of skin type II could only be acquired under very specific circumstances of prolonged exposure. Conversely, sun exposure on days with rounded UVI values of 2 can indeed provide doses sufficient to induce erythema in skin type II after two hours around noon. In conclusion, our analyses do not support the claim of harmlessness currently associated with the entire low UVI exposure category in public guidance on interpretation of the UVI.

UV Index monitoring in Europe

The UV Index was established more than 20 years ago as a tool for sun protection and health care. Shortly after its introduction, UV Index monitoring started in several countries either by newly acquired instruments or by converting measurements from existing instruments into the UV Index. The number of stations and networks has increased over the years. Currently, 160 stations in 25 European countries deliver online values to the public via the Internet. In this paper an overview of these UV Index monitoring sites in Europe is given. The overview includes instruments as well as quality assurance and quality control procedures. Furthermore, some examples are given about how UV Index values are presented to the public. Through these efforts, 57% of the European population is supplied with high quality information, enabling them to adapt behaviour. Although health care, including skin cancer prevention, is cost-effective, a proportion of the European population still doesn't have access to UV Index information.

Schoolyard Shade and Sun Exposure: Assessment of Personal Monitoring During Children's Physical Activity

Childhood exposure to ultraviolet radiation (UVR) is a major risk factor for the development of melanoma later in life. However, it is challenging to accurately determine personal outdoor exposure to UVR, specifically erythemally weighted UVR (UV_Ery ), due to technological constraints, variable time-activity patterns, and the influence of outdoor environmental design. To address this challenge, this study utilized mobile and stationary techniques to examine the UV_Ery exposures of 14 children in a schoolyard in Lubbock, TX, in spring 2016. The aims of the study were to examine the influence of artificial shade on personal UV_Ery exposures and to assess full sun exposure ratios (ERs) within the same playground microenvironment. On average, personal wrist dosimeters worn during play in the sun measured 18% of the total onsite UV_Ery measured by a stationary UV pyranometer. Shade was found to significantly reduce the personal UV_Ery exposures by 55%, UVB_{280-315 nm} exposures by 91%, and the overall solar radiation by 84%. Substantial benefits can be garnered through focused design of children's recreational space to utilize shade-both natural and artificial-to reduce UVR exposures during play, and to extend safe outdoor stays. Finally, although the wrist is a practical location for a dosimeter, it often underestimates full exposures, particularly during physical activity.

Novel approach to analysing large data sets of personal sun exposure measurements

Personal sun exposure measurements provide important information to guide the development of sun awareness and disease prevention campaigns. We assess the scaling properties of personal ultraviolet radiation (pUVR) sun exposure measurements using the wavelet transform (WT) spectral analysis to process long-range, high-frequency personal recordings collected by electronic UVR dosimeters designed to measure erythemal UVR exposure. We analysed the sun exposure recordings of school children, farmers, marathon runners and outdoor workers in South Africa, and construction workers and work site supervisors in New Zealand. We found scaling behaviour in all the analysed pUVR data sets. We found that the observed scaling changes from uncorrelated to long-range correlated with increasing duration of sun exposure. Peaks in the WT spectra that we found suggest the existence of characteristic times in sun exposure behaviour that were to some extent universal across our data set. Our study also showed that WT measures enable group classification, as well as distinction between individual UVR exposures, otherwise unattainable by conventional statistical methods.

Proposal for a modification of the UVI risk scale

Peak UVI values for the globe using a modified colour scale. With the colour scale for UVI as currently recommended by WHO, more than 78% of the globe area – representing 89% of the world's population – would be indistinguishable.