If you thought driving around your local town was difficult enough with all the traffic flow measures, speed bumps, and endless lights to navigate, spare a thought for the residents of Santiagio, Chile, who now have to pay attention to a new “traffic” signal: one that indicates the level of UV-radiation hitting their streets.
Why would you want to know that?
Well, if you’re Chilean, you’d probably be very interested to learn that recent studies have indicated that 18-year olds living near the equator can have absorbed as much ultraviolet radiation as seniors living in other parts of the world. And because the effects of UV-radiation exposure is cululative over a lifetime, this is a very serious finding. Skin cancer rates are soaring.
Ultraviolet radiation can be divided into three portions according to wavelength. UV-A, UV-B, and UV-C. The latter, the lowest wavelength of the three bands–and therefore the most energetic–would be very harmful to biological organisms if it ever got through the atmosphere. Fortunately it is stopped dead by ozone around the 35km altitude. UV-A on the other hand, usually reaches the surface, but because it is of much lower energy it is much less harmful, although may potentially cause genetic damage in high doses. UV-B comes in somewhere in between in its potential harm, and is most sensitive to changes in the thickness of the ozone layer.
So what’s the ozone layer, and why is it changing? Ozone is an unstable form of oxygen consisting of three oxygen atoms that is constantly formed and broken by the interaction of solar radiation with atmospheric oxygen. Its presence prevents the majority of the UV-B rays reaching the ground where it can cause sunburn. What’s particularly cool is that land-based life was only able to develop after ocean-based life photosynthesized for a good amount of time to produce the oxygen that lead to the protective ozone layer! The reason the ozone layer has depleted in recent decades is due to the reaction of ozone molecules with free radical catalysts that can be found in CFCs and other man-made compounds. Although 160 countries have signed a treaty to ban the production of CFCs, the long-life of these compounds mean that the ozone layer is still thinning.
The way the ozone layer changes over the Earth’s surface over time is a complicated matter depending on altitude, solar radiation levels, convection currents, and many other factors. To be safe, no matter where you are it’s best to follow the example of the Australians and Slip, Slop, Slap when the sun is out!