| Research Abstract |
It has been considered that the actinic ultraviolet rays of the sun are abruptly terminated by ozone and oxygen absorption. The first report of stratospheric ozone depletion was published in l985 [Farman et al., 1985]. In Japan, recent observations showed an increase of ultraviolet-B (UV-B) radiation(280-320 nm) resulting from human-induced decreases in stratospheric ozone [Japan Meteorological Agency, 1998 ; Sasaki et al., 1998]. Most of the concern over the increase of UV-B has arisen due to the prediction that this would have significant biological impact, including harmful effects on human health. If given qualities of ultraviolet assumed, the human dosage of ultraviolet would be multiplied or reduced by the reflectance and transmittance of ground cover materials. The basis of data is needed concerning spectral properties of these materials. The primary purpose here is to describe spectral properties of a plant leaf in the ultraviolet region, and suggest the possible benefits. The
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ultraviolet region of solar radiation is conveniently divided into segments A(320-400nm), B(280-320nm), and C(wavelengths shorter than 280nm), In the ultraviolet region (UV-A, UV-B, UV-C), reflectance of a green leaf was very low (around 5%), and transmittance was absolutely zero. A green leaf of plant absorbed a full 95% of the incident ultraviolet. The features in the ultraviolet region did not change from the inception of foliage in early spring, through the intense deep green of summer, to autumn coloration and falling leaves in winter, whereas they showed significant change in the visible and near-infrared regions. The results indicate, theoretically, that plant leaves are working as another terminator of harmful ultraviolet ray, protecting plants themselves and animals, including humans. Regarding biological diversity, organic design with plants within our living or working spaces should be considered in reducing ultraviolet ray. These urban designs would serve the integrated functions of cooling the urban heat island, creating beautiful landscapes, and reducing greenhouse gases like carbon dioxide (C02). Less
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