The purpose of my lecture is to present basic aspects of photoaging particularly
focussing on carcinogenic effect of solar ultraviolet (UV) radiation on human skin, based
on recent findings which contribute to better understanding of direct and indirect effects
of ultraviolet radiation (UV) on living cells.
Ozone depletion and UVB radiation on the ground level
The most important and convincing event caused by loss of ozone is an increase in
the amount of shorter UVB ranging 290 to 300 nm at the surface of the earch, since
O3 molecule can absorb efficiently UVC and UVB ranging 220 nm to 320
am as natural sunscreen.
In 1985, more than 40% decrease of the amount of ozone over Antarctica between
1977 and 1984, and in 1988, the decrease in ozone over the North Hemisphere were
indentified. The total reduction of ozone in the next 50 years is assumed to be upto
15% depending on the models to estimate the amount of chlorofluorocarbon (CFC) in the
atmosphere.
The Japan Meteorological Agancy (JMA) started the spectral observation of global
solar UV radiation at Tsukuba (36.05´N) since 1990, using the Brewer
spectrophotometers. JMA measures UV irradiance at the wavelength between 290 and
325 am with a wavelength interval of 0.5 nm.
Daily accumulation of UVB irradiance changes depending largely on local weather,
total ozone, atmospheric turbidity and solar zenith angle. From daily data, JMA reports a
monthly UVB dose regularly to give information of UVB trend in japan. JMA concluded
that there was no apparent increase of annual UVB dose in 1993 compared with those
of 1991, and 1992 (Fig. 1). Kerr et all, however, showed an upward trend of 300 nm
solar UVB at Toronto (44° N) by 35% per year in winter, and 7% per year in summer
based on the measurement of UVB between 1989 and 1993 (Fig. 2). Further they
confirmed no changes of UVA at 325 am which is not absorbed by ozone molecule.
They indicated that the downward trend in total ozone during these term at Toronto
may be responsible for an increase of 300 nm short UVB.
|