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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Within this study, the erythemal ultraviolet (UV) exposure received by different parts of the body during four different activities is determined. Optoelectronic devices were used to measure the erythemal UV exposure at 10 different positions of the body. The measuring devices were fixed on the forehead, on the shoulders, on the arms, on the chest, on the thighs and on the lower legs. The measurements were performed during the following activities of the test persons: walking, sitting, lying and sitting up. The measurements were performed on four clear sky days in the early afternoon at 1 s interval. One measurement sequence was taking 30–40 min. For the analysis of the measured UV exposures, the ambient UV is taken as a reference to remove the atmospheric fluctuations on the measured UV exposure. The strong dependence of the UV exposure on the activity and on the orientation of the test person is shown. Most of the body parts receive the highest exposure, when the test subject is sitting up or lying. The shoulders are most at risk when the test person is walking, whereas during the activities sitting up and lying the legs are most at risk.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The personal erythemal UV exposure of people as a function of their activity has already been investigated within several studies. The exposure of test persons was measured during typical leisure activities such as skiing (e.g. [1]), spending the time on the beach (e.g. [2]) playing tennis (e.g. [3]), cycling (e.g. [4]), and during urban environment leisure activities such as sitting in a beer garden or shopping [4]. Other studies concentrated on the exposure of outdoor workers such as gardeners (e.g. [5, 6]), lifeguards (e.g. [7, 8]) construction workers (e.g. [9, 10]) and farmers [11]. A question of interest was also how much children are at risk when they are at school [12]. One or two dosimeters were used in most of the investigations. These were fixed on the forehead, on the neck, on the chest, on the arms, on the back or on the wrist. With that, measured exposures are not directly comparable. The ratio of the personal UV exposure to the ambient UV (also called erythemal exposure ratio [ER]) is used to remove several influences on the UV exposure and to make exposure measurements more comparable. In general, the ER is within 0 and 1, but under certain conditions (e.g. high albedo, a position perpendicular to the sun) and for short periods the ER may exceed a value of 1. For example, Siani et al. [1] found an average ER value for skiers in Alpine region around 0.6 with minimum and maximum values between 0.26 and 1.46. In spring, the ER was noticeable higher, with an average value around 1.02 and maximum and minimum values of 0.46 and 1.72 respectively. A large variation in the average ER values for outdoor workers is found in literature. ER values between 0.09 and 0.27 were reported for gardeners and lifeguards [5-8]. For vineyards workers Siani et al. [13] obtained ERs between 0.19 and 0.87. Within a group of farmers, Schmalwieser et al. [11] found differences by a factor of 5 and differences by a factor of 1.5 by gender. A huge fluctuation of the ER between the different activities may therefore be noticed.

An open question concerns the differences of the UV exposure and the exposure incident on the different parts of the body. In a few studies, manikins were equipped with several dosimeters and exposure was measured for static positions (e.g. [14]). The present work focuses on exposure measurements on different body parts during dynamic activities with a high temporal resolution. The incident UV radiation on different parts of the body is investigated during walking, sitting, lying and sitting up.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Instrumentation

Measurements of the erythemal UV exposure were performed using the optoelectronic personal UV dosimeter type X2000-10 (Gigahertz, Germany). A description of its properties (spectral response, temperature sensitivity, etc.) can be found in Schmalwieser et al. [11]. These dosimeters allow the determination of the UV exposure as a function of time. The shortest measurement interval is 1 s. Ten dosimeters were mounted on a special suit (Fig. 1). Their readings are representative for the different body parts: forehead, shoulders, arms, chest, thighs and lower legs. The optoelectronic devices were calibrated and intercompared in the laboratory and in front of the sun (as described in Schmalwieser et al. [11]). The ambient erythemal UV exposure was measured by a Biometer Model 501 (SolarLight Inc, USA). This Biometer supplies the Austrian UVB network with erythemal UV data (e.g. [15]) and is serviced [16] according to international recommendations [17].

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Figure 1. Measurements of the UV exposures when the study subject was sitting up.

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Location and date of the experiments

This experimental study was performed at the campus of the Veterinary Medicine University of Vienna (48.25°N, 16.43°E, 150 m a.s.l.). The same measurement sequence was performed altogether seven times on 25 May, and from 12 to 14 July 2010. Six sequences of the seven were carried out under ideal clear sky conditions. Measurements were performed at solar elevations between 46° and 64°. Within one sequence, the study subject took always the same way starting first with a walk toward north-northeast (NNE), then turning toward east-southeast (ESE), then again toward NNE and then toward west-northwest (WNW). Afterward the test person sat down for a certain time and then moved the chair by 90° toward another sky direction. This was repeated three times so that the test person faced to four different sky directions. The volunteer then walked the way back (SSW) to the starting point. In the last part of the measurement sequence, the study subject laid down in the grass and sat up in the end (Fig. 1).

To clearly differentiate between the activities, the complete body of the study subject was covered with a black cloth between changes in activity and changes in direction (during coverage UV exposure was near to zero). The total duration of one measurement sequence was between 30 and 40 min. During the measurements, the study subjects were always in direct sun. The buildings in the surrounding are made of red bricks and the streets are made of asphalt. Red bricks, asphalt as well as the grass in between possess a low albedo. The buildings may also block a part of the diffuse radiation to a small certain extent.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Case study: 12 July, 13:00–13:35 Central European Time

Figure 2 shows one whole measurement sequence. Figure 3 shows measurements during walking toward NNE. The fluctuations of the UV exposure of the left arm show the influence of the movement—respectively of changes of the dosimeter's inclination. During this activity, the left part of the body was in direct sun which explains that the received UV exposure is higher on the left shoulder and on the left arm than on the right side. Figure 4a,b shows the UV exposure during sitting, walking toward SSW, lying and sitting up on 12 July, 13:10 Central European Time. Also during sitting, the study subject received the highest exposure on its shoulders. Figure 4a shows UV exposures measured during four sitting series with different orientations of the study subject. The second and third series show a more favorable orientation of the study subject to the sun. Figure 4b shows measurements for the three last activities of a sequence. During lying, the UV exposure on the left shoulder is very low whereas the right leg and the forehead receive more UV. When the study subject sits up, a strong increase in the UV exposure on the chest and on the forehead may be noticed. The inclination of the body parts is the first factor that influences the angle of incidence of the direct sun on the dosimeter. The second factor is the orientation of the body in respect to the sun.

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Figure 2. Measurement on July 12th, 13:00–13:35 Central European Time (sun height = 57° to 60°).

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Figure 3. First measurement sequence: walking toward NNE (sun : sun height = 60°, SSW).

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Figure 4. (a) Measured UV irradiance while sitting, facing four different directions (July 12th, 13:15 Central European Time (CET), sun height = 60°, SSW). (b) Measured UV irradiance while walking toward SSW, lying and sitting up (July 12th, 13:25 CET, sun height = 59°, SW).

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Figure 5 shows the UV exposure on the forehead in terms of the ER during walking as a function of the walking direction. This is shown for four measurements. The lowest ER was measured when the study subject was walking toward NNE direction. For the other walking directions, the measured UV exposure is two to three times higher. An orientation of the dosimeters toward SW clearly leads to a higher UV exposure. Further analysis (data not shown here) showed that some body parts, such as the arms, received a maximum UV exposure that is six times higher than the minimum exposure.

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Figure 5. UV exposure ratio on the forehead while walking in four different directions. Four measurements are shown. The walking direction is indicated on the x-axis. The sun position including sun elevation and azimuth is indicated by the different symbols.

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Average UV exposure

The mean ERs of the different body parts are shown in Fig. 6 as a function of activity for all the six clear sky measurements. These mean ERs denote a random orientation of the study subject. It is not taken into account that the study subject walked for a longer time in NNE direction than in ESE direction. During walking, the study subject receives the highest exposures on the shoulders which is 70% higher than the exposure of the chest and the forehead. During sitting the highest UV exposures are received by the thighs and the shoulders. Exposures are 60% higher than on the forehead and on the chest. During sitting up and lying, the exposures are highest on the lower legs (respectively 115 and 55% higher than on forehead).

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Figure 6. UV exposure ratio as a function of activity for the different body parts. The mean of the six measurements performed during the clear sky days is shown. The bars indicate the range of exposure during all measurements. The black dots indicate the mean exposure ratio.

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

In this study, we have shown that optoelectronic dosimeters have a large potential: Movements of legs and arms during walking lead to short fluctuations of the measured UV exposures and could therefore clearly be distinguished. Differences of the UV exposures on the different body parts were identified too. These differences are reproducible as they are associated with the type of activity and with the orientation of the study subject in respect to the sun.

The dosimeters are mounted on a suit and additionally fixed by rubber bands, which are—like all the textiles—bendable. Their inclinations and orientations may therefore only be adjusted with an accuracy of roughly ±10%. This may influence the measurements.

ER values obtained within the scope of this study are between 0.05 and 1. They are comparable with ER measured by other groups and reported in the literature [1-14]. The highest ERs occurred on the lower legs while lying and sitting up. In these positions, the lower legs are oriented horizontally like the device for ambient UV measurements. This shows that the influence of the surrounding (line of horizon and albedo) was relatively low in the chosen environment. High ERs were found also on the shoulders. The head however obstructs a noticeable part of the sky and may reduce the exposure of the shoulders. A similar situation is found for the thighs during sitting. The noticeable lower ER values on vertical body parts like the forehead can be explained by the relatively high solar elevation and the reduced diffuse radiation as an essential part of the field of view is the ground.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

This study was partly supported by the EC Framework 7 funded ICEPURE project (Framework Programme 7: ENV.2008.1.2.1.5. Quantification of changing surface UV radiation levels and its impact on human health, 227020).

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References