Scattered UV Beneath Public Shade Structures During Winter¶ (original) (raw)
Related papers
Ambient ultraviolet radiation levels in public shade settings
International Journal of Biometeorology, 1999
As people become better informed about the harmful effects of prolonged exposure to solar ultraviolet radiation (UVR, 280-400 nm) they will seek the protection of shade, particularly in tropical locations such as Townsville (19°south). Using broad-band radiation sensors for solar ultraviolet-B (280-315 nm), ultraviolet-A (315-400 nm) and daylight (400-800 nm) radiation, the exposure levels were measured in both the horizontal (shaded and unshaded) and vertical (shaded and unshaded) directions. The measurements were conducted at eight locations (shade settings) in Townsville during the period between December 1997 (summer) and May 1998 (beginning of winter). The quality of protection was assessed by the ratio of unshaded to shaded radiation exposure, the UVB/shade protection ratio (UVB-SPR). The UVB-SPR varies considerably between the different shade settings, with a beach umbrella showing the least protection and dense foliage the highest protection. The roof of a house verandah can provide only little protection if the verandah catches the afternoon sun. Increasing cloud cover decreases the UVB-SPR for all settings because of the increase in the diffuse fraction of the radiation. Only one setting provided a UVB-SPR of 15 or higher, as suggested for protective shading against solar UVB radiation. Shade from direct sunlight alone does not provide enough protection against high levels of solar UVR. Apart from the transmission qualities of the shading material, it is the construction of the whole shade setting that determines the exposure levels underneath. A shade structure with enough overhang is recommended so that high levels of scattered radiation do not reach the skin.
Increasing the ultraviolet protection provided by shade structures
Journal of Photochemistry and Photobiology B: Biology, 2005
The side openings of a shade structure have a direct influence on where the shade is located and the level of scattered UV in the shaded area. UV exposures were assessed for the decrease in scattered UV beneath specific shade structures by the use of two types of side-on protection, namely, polycarbonate sheeting and evergreen vegetation. Dosimetric measurements conducted in the shade of a scale model shade structure during summer and winter showed significant decreases in exposure of up to 65% for summer and 57% for winter when comparing the use and non-use of polycarbonate sheeting. Measurements conducted in the shade of four shade structures with various amounts of vegetation covering different sides, showed that adequate amounts of and positioning of vegetation decreased the scattered UV in the shade by up to 87% for the larger solar zenith angles (SZA) of approximately 67 o and up to 30% for the smaller SZA of approximately 11 o when compared to the shade structure that had no surrounding vegetation.
Building and Environment, 2019
A method was proposed for calculating the ultraviolet protection factor (PF) of small to medium built shade structures. The method takes into account the amount of sky view visible from under the structure, the transmittance of the roof material, the relative amount of diffuse ultraviolet radiation (UV), the measurement position under the structure and the albedo of the relevant surfaces. The PF of four different shade structure designs was measured 90 cm above ground-level at the centre of the widest diameter of each structure. Measurements were only made on cloudfree days. Three structures had a thin metal roof and the fourth had shade-cloth. The proportion of sky view ranged from 4.6% to 15.4% for these structures. The influence of position was investigated for one structure, with the PF evaluated 50 cm in from each of the sides at 90 cm above ground-level. The reliability of the method was tested by comparing calculated and measured PF values for solar zenith angles ranging from 7 o to 49 o. The mean absolute difference between the calculated and the measured PF for these small to medium structures was 1.4 PF (14%). The proposed method is more likely to be widely used to measure the PF in situ compared to measuring UV in full sun and in the shade with a UV meter because many stakeholders do not have access to UV meters due to the cost or the degree of specialization required to use these meters effectively.
Personal exposure distribution of solar erythemal ultraviolet radiation in tree shade over summer
Physics in Medicine and Biology, 2000
The personal radiant exposure distribution of solar erythemal UV in tree shade for an upright posture was measured, with measurements over the whole summer for a total of seventeen trees. For each tree, the personal radiant exposure distribution was measured for both the morning and afternoon periods. The exposure ratios averaged over all the trees and over the morning and afternoon periods ranged from 0.16 to 0.49 for the different anatomical sites. A numerical model was employed to estimate the UV radiant exposure to humans in the tree shade over the entire summer. The body sites with the higher exposure ratios in the tree shade were the vertex of the head, shoulders and forearms with radiant exposures over the summer of 1,300 MED to the vertex of the head and 1,100 MED to the shoulders and forearms. These radiant exposures in the shade are substantially higher than the ambient erythemal UV measured in full sun on a horizontal plane over a full summer at a more temperate Northern Hemisphere latitude. The average radiant exposures per day to each anatomical site for a complete day in the tree shade ranged from 4.6 to 14.6 MED. The research has provided new data that is essential to quantify the human UV exposure during outdoor activities. Airey D K, Wong J C F and Fleming R A 1995 A comparison of human-and headformbased measurements of solar ultraviolet B dose Photodermatol. Photoimmunol. Photomed. 11 155-158 Davis A, Deane G H W and Diffey B L 1976 Possible dosimeter for ultraviolet radiation Nature, 261 169-170 Diffey B L 1989 Ultraviolet radiation dosimetry with polysulphone film Radiation Measurement in Photobiology ed B L Diffey (Academic Press: New York) pp 136-159 Diffey B L 1992 Stratospheric ozone depletion and the risk of non-melanoma skin cancer in a British population Phys. Med. Biol. 37 2267-2279 Gies P, Roy C, Toomey S, MacLennan R and Watson M 1995 Solar UVR exposures of three groups of outdoor workers on the Sunshine Coast, Queensland Photochem. Photobiol. 62 1015-1021 Gies P, Roy C, Toomey S, MacLennan R and Watson M 1998 Solar UVR exposures of primary school children at three locations in Queensland Photochem. Photobiol. 68 78-83 Grant R H 1997 Biologically active radiation in the vicinity of a single tree Photochem. Photobiol. 65 974-982 Herlihy E, Gies P H, Roy C R and Jones M 1994 Personal dosimetry of solar UV radiation for different outdoor activities Photochem. Photobiol. 60 288-294 Holman C D J, Gibson I M, Stephenson M and Armstrong B K 1983 Ultraviolet irradiation of human body sites in relation to occupation and outdoor activity:
Photochemistry and Photobiology, 2004
To reduce ultraviolet radiation (UVR) exposure during childhood, shade structures are being erected in primary schools to provide areas where children can more safely undertake outdoor activities. This study to evaluate the effectiveness of existing and purpose built shade structures in providing solar UVR protection was carried out on 29 such structures in 10 schools in New Zealand. Measurements of the direct and scattered solar UVR doses within the central region of the shade structures were made during the school lunch break period using UVR-sensitive polysulfone film badges. These measurements indicate that many of the structures had UVR protection factors (PF) of 4-8, which was sufficient to provide protection during the school lunch hour. However, of the 29 structures examined, only six would meet the suggested requirements of UVR PF greater than 15 required to provide all-day protection.
Estimation of Pedestrian Level UV Exposure Under Trees¶
Photochemistry and Photobiology, 2007
fields in open-tree canopies where the spacing between trees is equal to or greater than the width of individual tree crowns. The model predicted the relative irradiance (fraction of above-canopy irradiance) under both sunlit and shaded conditions under clear skies with a mean bias error of less than 0.01 and a root mean square error of 0.07. Both model and measurements showed that the locations people typically perceive as shady, low-irradiance locations in the environment can actually have significant UV-B exposure (40-60% of that under direct sunlight). The relationship of tree cover in residential neighborhoods to erythemal UV-B exposure for children and adults was modeled for the 4 h around noon in June and July. Results showed that human exposures (on the horizontal) in cities located at 15 and 30؇ latitudes are nearly identical. For latitudes between 15 and 60؇, ultraviolet protection factors (UPF) were less than 2 for less than 50% tree cover. A UPF of 10 was possible at all latitudes for tree cover of 90%. ¶Posted on the web site on January 28, 2002. Abbreviations: G, foliage projection area; I b0 , above-canopy direct beam radiation; I d0 , above-canopy diffuse radiation; I min , minimum measured below-canopy irradiance; I p , modeled below-canopy relative irradiance; I r , measured below-canopy relative irradiance; I 0 , above-canopy irradiance; M, tree cover fraction; MBE, mean bias error; MED, minimum erythemal dose, N, sky radiance distribution; P o , probability of unobstructed direct beam radiation below canopy; P o Ј, probability of unobstructed diffuse radiation below
Seasonal variation of facial UV exposures in the shade
The personal distribution of solar erythemal UV exposures to the face, head and neck was investigated for a public shade structure in the seasons of winter and summer. Calculated personal erythemal UV exposures in the shade during winter ranged from 0.3 SED per day for the top of the head to 1.8 SED per day for the chin. In comparison, erythemal UV exposures in the shade during summer ranged from 0.3 SED per day for the top of the head to 4.6 SED per day for the chin. Broadband global and diffuse erythemal UV was also measured on a horizontal plane in the open at five minute intervals during the winter and summer period. Cumulative daily global and diffuse erythemal UV exposures for winter were 22±3.8 SED and 14±3.0 SED, respectively. While, cumulative daily exposures for summer were 55±13.6 SED and 42±3.1 SED for global and diffuse erythemal UV respectively. From this research it can be concluded that anyone seeking shade under this common public shade structure for an extended per...
Protection Factor of small to medium sized built shade structures 2 3
2018
A method was proposed for calculating the ultraviolet protection factor (PF) of small to medium built shade structures. The method takes into account the amount of sky view visible from under the structure, the transmittance of the roof material, the relative amount of diffuse ultraviolet radiation (UV), the measurement position under the structure and the albedo of the relevant surfaces. The PF of four different shade structure designs was measured 90 cm above ground-level at the centre of the widest diameter of each structure. Measurements were only made on cloudfree days. Three structures had a thin metal roof and the fourth had shade-cloth. The proportion of sky view ranged from 4.6% to 15.4% for these structures. The influence of position was investigated for one structure, with the PF evaluated 50 cm in from each of the sides at 90 cm above ground-level. The reliability of the method was tested by comparing calculated and measured PF values for solar zenith angles ranging from 7 o to 49 o. The mean absolute difference between the calculated and the measured PF for these small to medium structures was 1.4 PF (14%). The proposed method is more likely to be widely used to measure the PF in situ compared to measuring UV in full sun and in the shade with a UV meter because many stakeholders do not have access to UV meters due to the cost or the degree of specialization required to use these meters effectively.
Comparison of the spectral biologically effective solar ultraviolet in adjacent tree shade and sun
Physics in Medicine and Biology, 1999
The solar spectral UVR irradiances in tree shade and sunlight have been measured in a sub-tropical southern hemisphere summer. The spectral data allowed the UVB and UVA irradiances and the biologically effective irradiances to be calculated for different harmful biological processes to human skin and eyes. The average of the ratio of the UVA to UVB irradiances was lower by 26% in the shade compared with the same ratio in the sun. The spectral shade ratio calculated as the ratio of the spectral biologically effective irradiances in the shade to those in the adjacent sun decreased with increasing wavelength for all of the trees. The decrease in the shade ratio was approximately 42% at 400 nm compared with the shade ratio at 300 nm. Despite the UVR protection provided by tree shade, the erythemal UVR exposure received in 1 h in the tree shade exceeded the occupational limit for UVR exposure.