You should wear a hat here in summer.
But wait, stay with me for a moment. It will be worth it . . .
Most oxygen in the atmosphere is in the form of O2 where two oxygen atoms are double-bonded together. But oxygen also exists as O3, commonly called ozone (often smelled during a lightning storm) which is a highly reactive form of oxygen consisting of three oxygen atoms bonded together.
For a number of reasons, this process predominantly only occurs at a certain level of the stratosphere (15-50 km high) creating an ozone layer surrounding the earth.
Ozone strongly absorbs long wavelength UV radiation from the sun which at full intensity would be lethal to life on earth. And as such, the ozone layer described above provides a protective layer or radiation shield for life on earth.
Refrigeration technology, that is the technology to keep things cool or cold such as in refrigerators and air conditioning, works by continuously circulating a chemical substance, refrigerant, through a closed system. Simply put, when the refrigerant evaporates, it removes heat from a source such as the inside of a refrigerator, and then when the refrigerant is compressed, it releases this heat, in this case, outside or external to the refrigerator. The refrigerant goes round and round the closed system removing and releasing heat with energy being needed to run the compressor.
Few chemical substances fit all the criteria of an efficient refrigerant. Chlorinated fluorocarbons (CFCs) were discovered in the 1930s and were the ideal refrigerant and revolutionized refrigeration. They also began to be extensively used as propellants in all sorts of aerosols. Not only were CFCs non-reactive, non-toxic and non-flammable but also they were cheap to produce.
ANTARCTIC OZONE HOLE
CFCs, however because of their inert, unreactive nature, did not go away. Instead when released they concentrated in the stratosphere and in the 1970s research was done suggesting that CFCs are decomposed by sunlight to produce chlorine which breaks down ozone. It was postulated that this could deplete the protective ozone layer surrounding the earth in the range of 1-5% according to some predictions.
As predicted there was a gradual overall depletion in the ozone layer above the earth, but in 1985, data was brought to light showing a significant depletion of the ozone layer over Antarctica each spring from 1974 to 1985 ranging up to 60%! It was puzzling to scientists why a depletion of this magnitude would occur only during a few month period and only in a specific geographic location. Initially the term Antarctic Ozone Hole was actually a misnomer since it was rather a relative periodic depletion. However since 1990, a true hole in the layer has developed each spring.
The science of why this hole develops over the poles (one has also developed over the Arctic Pole) is complicated but has to do with polar stratospheric clouds and the time of the year where enough sunlight is present in combination to cause the requisite chemical reactions in the stratosphere. This mainly occurs in the spring.
Because of these developments, the international community banded together and the use of CFCs was curtailed by the Montreal Protocol of 1987.
Where are we now? Ozone levels have been gradually increasing since the reduction in production and use of CFCs and related compounds. It is estimated that the overall ozone layer and the Antarctic Ozone Hole will take about 50 years to recover.
SKIN CANCER IN NEW ZEALAND
The ozone hole over Antarctica has at times grown so large as to allow increased levels of radiation to reach parts of South America, Australia and New Zealand. This includes increased levels of UVB (Ultraviolet B) radiation which is a contributory factor to skin cancer including malignant melanoma, a type of skin cancer with a particularly high mortality rate.
Do you remember the ABCDE of melanoma—what to watch for? A is for asymmetry, that is, if you draw a line through the lesion, the two halves won’t match. B is for border. The edges of an early melanoma tend to be uneven, scalloped or notched. C is for color. Melanomas often have a variety of colors or different shades of colors in them. D is for diameter. Melanomas are generally bigger than 6 mm, the size of an eraser on a pencil. E is for evolving which means changing—any change in size, shape, color or new symptom such as bleeding or itching. You obviously don’t need all of these above signs. Any of them means you need to get checked.
Studies have shown increased levels of skin cancer in regions with decreases in the ozone layer and higher UVB levels. While the Antarctic Ozone Hole is not directly above New Zealand, when it breaks up filaments of ozone-poor air can pass overhead.
The most common cancer in New Zealand is skin cancer and New Zealand has one of the highest rates of skin cancer in the world. This is due to high levels of ultraviolet radiation in the summer months, a high proportion of people of European ancestry with fair skin, an outdoor lifestyle and depletion in the ozone layer.
You should wear a hat here in the summer.