الفهرس 
Effect of ultraviolet radiation on human healthOnly 14 pages are availabe for public view
 |  | from | 323 |  |  |
| | | from | 323 | | |
Abstract
Tropospheric ozone is also highly variable in time, both seasonal and
daily scales. Owing to the photochemical mechanisms that synthesize
ozone, minimum ozone concentration is usually found early in the
morning, while the maximum value is set in late afternoon. Changes in
tropospheric ozone from day to day can be as large as a factor of 2 or 3.
Regarding long-time trends, the WMO (1994) estimates an enhancement
of boundary layer ozone levels of up to 50% in some populated Northern
Hemisphere regions; Janach (1989) estimates a global averaged increase
of 1–2% for tropospheric ozone between the 1960s and 1989; and the
Intergovernmental Panel on Climate Change, IPCC (2001) assigns a small
but significant positive radiative forcing to increased tropospheric ozone concentration, which is estimated to be some 8 DU between 1750 and
current days. Although tropospheric ozone is very variable both in time
and space, it has been suggested that in industrial areas of the Northern
Hemisphere increased tropospheric ozone can overcompensate (as far as
filtering UV-B is concerned) for stratospheric ozone depletion (Brühl and
Crutzen, 1989).
The sensitivity of erythemal ultraviolet (EUV), will be discussed later,
to atmospheric ozone is frequently expressed with the radiation
amplification factor (RAF), also called sensitivity by Madronich (1992)
or magnification factor by Bais et al. (1993a), defined as the percentage
increase in EUV that would result from a 1% decrease in the column
amount of atmospheric ozone (McKenzie et al., 1991; Madronich, 1995a ;
Madronich et al., 1995b; Durzan and Smertenko, 2005). For that aim, the
RAF has become a widely used standard index during last years
(McKenzie et al., 1991; Madronich, 1993b; Bodhaine et al., 1997;
Madronich et al., 1998; Dubrovsky, 2000; Zerefos, 2002, Serrano et al.,
2008).