Few may have noticed but for the past year the Meteorological Office of Malta International Airport, in collaboration with the Department of Dermatology of Sir Paul Boffa Hospital, has been publishing a six-day ultra violet radiation forecast or UV index.
The sun is actually a very large star, weighing over 300,000 times more than our planet, earth. The sun is over 149,600,000 kilometres away from us, yet we can still see it clearly!
The sun gives off energy, or rays, that provide us with the heat and light we need to stay alive. One type of ray that comes from the sun is an infrared ray - what makes the sun feel warm on our skin.
The other types of rays that come from the sun are ultraviolet radiation or UV, in particular UVA, UVB and UVC. We cannot see or feel UV radiation as it is invisible and does not feel hot on our skin.
UVC is extremely dangerous, but it is completely absorbed by the ozone layer, a protective thin ring of gas that stops it completely from reaching the surface of the earth.
UVB is mostly absorbed by ozone, although some reaches the surface of the earth under normal conditions and even more will reach the surface because of ozone depletion. Relatively small changes in the thickness of the ozone layer can lead to significant changes in the amount of UVB radiation reaching the earth's surface.
UVB causes our skin to get sunburnt and it is particularly effective at damaging DNA, causing melanoma and other types of skin cancer.
It does not need to be warm or sunny for UV radiation to burn our skin. In fact, most people get sunburnt even when the temperature is between 17 and 27 degrees.
It has also been linked to damage to some materials, crops and marine organisms. It is always important to protect oneself against UVB, even in the absence of ozone depletion, by wearing hats, sunglasses and sunscreen.
However, these precautions will become more important as ozone depletion worsens. UVA is not absorbed by ozone. UVA rays are mainly responsible for inducing skin aging. Besides wrinkling the human skin, it also plays an important part in the formation of photochemical smog and also in fading and damage to plastics, paints and fabrics.
Therefore, the UV radiation reaching the earth's surface is largely composed of UVA with a small UVB component.
Stratospheric ozone is a particularly effective UV radiation filter and absorber. As the ozone layer gets thinner, the protective filter provided by the atmosphere is progressively reduced. Consequently, human beings and the environment are exposed to higher UV levels, and especially higher UVB levels that have the greatest impact on human health, animals, marine organisms and plant life.
The amount of UV-B received at a particular location is strongly dependent on:
¤ Sun height: the higher the sun is in the sky, the higher the UV level. Thus, UV radiation varies with time of day and time of year, with maximum levels occurring when the sun is directly overhead, that is between 11 a.m. and 3 p.m. during the summer months.
¤ Latitude: the closer to the equator, the higher the UV levels. As at the polar regions, the sun is always low in the sky; sunlight passes through more of the atmosphere, so more of the UV-B is absorbed. For this reason, average UV-B exposure at the equator is over 1,000 times higher than at the poles.
¤ Cloud cover: UV levels are highest under cloudless skies. Even with cloud cover, UV levels can be high due to the scattering of UV radiation by water molecules and fine particles in the atmosphere.
¤ Altitude: at higher altitudes, a thinner atmosphere filters less UV radiation. With every 1,000 metres increase in altitude, UV levels increase by 10 to 12 per cent.
¤ Ozone: ozone absorbs some of the UV radiation that would otherwise reach the earth's surface. Ozone levels vary over the year and even across the day.
¤ Ground reflection: UV radiation is reflected or scattered to varying extents by different surfaces; for example, snow can increase UV radiation by as much as 80 per cent, dry beach sand by about 15 per cent and sea foam by about 25 per cent.
Most people are used to adjusting their daily plans and choice of clothing to the weather forecast, especially to temperature predictions.
The UV index, published on the Malta International Airport website, gives an indication of the potential danger of sun exposure. These values can help individuals make healthy choices.
The UV index
0 - 2: Minimal - wearing a hat is sufficient protection.
3 - 4: Low - wearing a hat and a sunscreen with, at least, SPF 20, is recommended.
5 - 6: Moderate - wearing a hat, a sunscreen with, at least, SPF 20 and staying in the shade is recommended.
7 - 9: High - In addition to the precautions recommended above, it is advised to stay indoors between 11 a.m. and 3 p.m.
10 +: Very High - In addition to the precautions recommended above, it is advised to stay indoors if possible.
More information about the UV index, as well as a continuously updated weather information and forecast service, is available on website http://www.maltairport.com/weather".
Mr Porter is chief meteorological officer, Malta International Airport plc