The "o" Zone.

INTRODUCTION

For several decades, atmospheric ozone, especially the stratospheric layer, has been known for its important protective role against the incoming solar ultraviolet radiation. In general, there is a natural balance between the ozone's production and its destruction with a net ozone surplus. Under the natural equilibrium, there are small dosages of solar ultraviolet radiation to which populations, living organisms, plants, and aquatic systems have generally become adapted. The harmful effects are thus generally very small except perhaps in the tropical/equatorial region. The surface dosage of natural ultraviolet radiation increases by many folds in going from high/mid latitudes to the equator. Because people living in the high dosage tropical belt have a darker skin tan which provides greater protection to the skin against ultraviolet radiation, this high UV radiation situation has not been considered particularly seriously in terms of adverse health and environmental effects that might occur in these regions.

The ozone layer suddenly came into scientific prominence about 12 years ago when it was realized that certain human activities may lead to significant ozone depletion from the naturally balanced level, thereby increasing the surface dosage of ultraviolet radiation leading to increased skin cancer and many other adverse biological, environmental, and climatic effects. Since any such ozone destruction would spread out globally, the net UV radiation effect would be most serious in the equatorial and tropical belt when already the ozone column thickness is minimum and ultraviolet radiation penetration is maximum. But perhaps even a more fundamental issue is to ascertain whether the already high UV radiation dosages received at the lower latitudes are contributing to tropical diseases and medical problems. Whether the 5 to 10 times higher dosages (in absolute terms) that would be received in the low latitude region in comparison to the higher latitudes (if a certain fraction of ozone column is reduced) would bring the radiation level above a certain threshold is another aspect relevant to the tropics. In other words, the "ozone modification" issue is of serious importance to the low latitude countries. The whole issue of ozone layer protection is thus indeed of global dimension. Yet, there is very little apparent involvement of scientists from the developing countries in the "ozone layer-ultraviolet radiation" work. While financial constraints may account for some of this non-involvement, lack of proper understanding of the effects at the public, scientific, and political levels is also a serious factor. Nevertheless, in the coming years, it should be appropriate to examine the "ozone layer-UV-B" matter in the specific context of tropical countries.

TYPICAL CONDITIONS

In order to examine the relevance of the ozone layer issue for the developing countries in the equatorial/tropical region, it would be helpful to summarize the atmospheric ozone and solar ultraviolet radiation influx globally. The seasonal distribution of vertical ozone column for different latitudes is shown in Figure 1. It is clear that at the lower latitudes, not only the ozone column thickness is significantly small but it also does not vary much seasonally. The solar ultraviolet radiation penetration is thus maximum at the lower latitudes throughout the year. The overall effect of the low ozone content coupled with smaller seasonal change