Ozone

Dramatic loss of ozone in the lower stratosphere over Antarctica was first noticed in the 1970’s by a research group from the British Antarctic Survey (BAS) who were monitoring the atmosphere above Antarctica from a research station.

The Halley Research Station BAS research stations in the Antarctic

Rumor has it that when the first measurements were taken in 1985, the drop in ozone levels in the stratosphere were so dramatic that at first the scientists thought their instruments were defective. Replacement instruments were built and flown out.  It wasn’t until they confirmed the earlier measurements, several months later, that the ozone depletion observed was accepted as genuine.

Evidence that human activities affect the ozone layer has been building up over the last 20 years, ever since scientists first suggested that the release of chlorofluorocarbons (CFCs) into the atmosphere could reduce the amount of ozone over our heads.

The breakdown products (chlorine compounds) of these gases were detected in the stratosphere. When the ozone hole was detected, it was soon linked to this increase in these chlorine compounds. The loss of ozone was not limited to the Antarctic. Around the same time the first firm evidence was produced that there had been an ozone decrease over the heavily populated northern mid-latitudes (30-60N). However, unlike the sudden and near total loss of ozone over Antarctica at certain altitudes, the loss of ozone in mid-latitudes is much less and much slower. Only a few percentage per year.

What Is Ozone And How Is It Formed?

Ozone (O3 : 3 oxygen atoms) occurs naturally in the atmosphere. The earth’s atmosphere is composed of several layers. We live in the “Troposphere” where most of the weather occurs; such as rain, snow and clouds. Above the troposphere is the “Stratosphere”; an important region in which effects such as the Ozone Hole and Global Warming originate. Supersonic jet airliners such as Concorde fly in the lower stratosphere whereas subsonic commercial airliners are usually in the troposphere. The narrow region between these two parts of the atmosphere is called the “Tropopause”.

Ozone forms a layer in the stratosphere, thinnest in the tropics (around the equator) and denser towards the poles. The amount of ozone above a point on the earth’s surface is measured in Dobson units (DU) – typically 260 DU near the tropics and higher elsewhere, Though there are large seasonal fluctuations, It is created when ultraviolet radiation (sunlight) strikes the stratosphere, dissociating (or “splitting”) oxygen molecules (O2) to atomic oxygen (O). The atomic oxygen quickly combines with further oxygen molecules to form ozone.

It’s ironic that at ground level, ozone is a health hazard , it is a major constituent of photo chemical smog. However, in the stratosphere we could not survive without it. Up in the stratosphere it absorbs some of the potentially harmful ultra-violet (UV) radiation from the sun (at wavelengths between 240 and 320 nm) which can cause skin cancer and damage vegetation, among other things.

The Ozone Hole often gets confused in the  press and by the general public with the problem of global warming. While there is a connection because ozone contributes to the greenhouse effect, the Ozone Hole is a separate issue. However it is another  reminder of the effect of man’s activities on the environment.

Over Antarctica (and recently over the Arctic), stratospheric ozone has been depleted over the last 15 years at certain times of the year. This is mainly due to the release of manmade chemicals containing chlorine such as CFC’s (ChloroFluoroCarbons), but also compounds containing bromine, other related halogen compounds and also nitrogen oxides (NOx). CFC’s are a common industrial product, used in refrigeration systems, air conditioners, aerosols, solvents and in the production of some types of packaging. Nitrogen oxides are a by-product of combustion processes, eg aircraft emissions.The current levels of depletion have served to highlight a unexpected degree of instability of the atmosphere, and the amount of ozone loss is still