Why is ozone considered a polar molecule

Ozone layer

It happens far above our heads, about 15 to 35 kilometers high in the stratosphere: Here the energy of sunlight splits the oxygen into its two oxygen atoms. The individual oxygen atoms react with each other and can also come together in a pack of three. If that happens, ozone molecules are created.

Because the ozone is concentrated in the stratosphere, a layer forms here: the ozone layer. This blocks a large part of the sun's rays and prevents too much ultraviolet radiation from reaching the earth. This is vital because the high-energy ultraviolet rays of the sun can destroy the cells of animals and plants and damage human skin. If the ozone layer in the stratosphere is intact, it acts like a huge protective screen against aggressive UV radiation.

Especially on hot summer days and when there is heavy traffic with a lot of exhaust gases, ozone can also be formed close to the earth's surface. Down here, however, the gas is not useful; it is harmful: it can cause headaches, tiredness, and stinging eyes, and it can attack the airways. If the ozone content on the ground exceeds a certain value, ozone warnings have been issued on the radio, television and the Internet for several years. Then physical exertion in the open air should be avoided.


One of the worst environmental catastrophes could just be prevented: Current measurements confirm that the ozone layer is becoming thicker again. The increase in carcinogenic UV radiation is thus stopped. But it is still too early to give the all-clear.

The new measurement data sound encouraging: exposure to UV radiation is decreasing. Up to 4% less of the harmful UVB rays reach the earth. Twelve measuring stations in Europe, Canada and Japan were evaluated for this purpose. The good news is the result of successful environmental policy. In the Montreal Protocol of 1987, measures to protect the ozone layer were agreed. This included the gradual ban on the destructive chlorofluorocarbons, or CFCs for short. Since then, the concentration of CFCs in the air has gradually decreased. The ozone layer can recover very slowly.

However, the skin should still be well protected. Sunscreens with a medium to high sun protection factor are still beneficial. Scientists warn that radiation exposure is particularly high in spring. Because CFCs only degrade very slowly. It gets really aggressive when it's very cold. The ozone layer over the poles is therefore still very thin. If the polar air masses shift to Europe in late winter and spring, then the effects of the ozone hole can also be felt in this country. Especially on these days there is an increased risk of sunburn.

So there is still no time to breathe a sigh of relief: Despite falling CFC levels, a hole in the ozone layer was discovered for the first time over the Arctic in 2011. Experts cite climate change as the reason for this: the temperature on the ground is increasing, but the stratosphere is cooling. The falling temperatures would cause the ozone to break down more quickly in the upper layers of the air.

The discovery of the ozone hole

In May 1985, an article in the journal “Nature” woke the public: “Heavy losses of total ozone in Antarctica” was the headline. British researchers had discovered a huge hole in the ozone layer over the South Pole, the size of the whole of Antarctica. The three authors of the article also included the geophysicist Joseph Farman, who is now considered the discoverer of the ozone hole. He had evaluated the measurements over the Antarctic station over a longer period of time.

There had been indications of the depletion of the ozone layer for a long time, but these were simply dismissed as measurement errors. With the appearance of the article, however, an alarm signal was triggered that no one could ignore. The international community reacted: In 1987, the so-called Montreal Protocol decided to withdraw the ozone killer chlorofluorocarbons from circulation.

The layers of the atmosphere

Similar to the floors of a multi-storey house, the atmosphere is divided into several layers. These layers have different properties - let's start on the "ground floor":

Dark storm clouds or blue skies, gentle breezes or strong winds: almost all weather events take place up to a height of 15 kilometers. This lower layer of the atmosphere is therefore also called the weather layer. Scientists say Troposphere to. About 90 percent of all air and almost all of the water vapor in the earth's atmosphere are contained in this layer. The higher the position in the troposphere, the colder it gets: At its upper limit, icy temperatures of up to minus 80 degrees Celsius prevail.

In the layer above, the stratosphere, the temperature suddenly rises again. At an altitude of around 50 kilometers, the thermometer even reaches a value of around 0 degrees Celsius. The reason for this warming is the ozone layer, which lies within the stratosphere. This works like a heater: it absorbs the sun's UV radiation and converts it into heat.

Above the stratosphere lies at an altitude of 50 to 80 kilometers Mesosphere. Because this layer does not contain ozone, it becomes bitterly cold again, down to minus 100 degrees Celsius. This makes the mesosphere the coldest layer in the atmosphere. Here dust particles and smaller rocks from space are stopped, which would otherwise fall to earth as meteorites. We can sometimes see these celestial bodies as shooting stars in the sky at night.

The air is getting thinner and thinner above the mesosphere. The gravity weakens with increasing altitude and can therefore hold the gas particles less and less. So that forms Thermosphere a smooth transition into space over hundreds of kilometers. The thermosphere takes its name from the high temperatures that prevail here: They rise up to 1700 degrees. In our opinion, however, it is not hot, because too few gases are buzzing around for the feeling of heat.

Ozone hole

High up in the stratosphere, the ozone layer protects us from harmful UV rays. If it didn't exist, the sun's rays would literally roast us on the ground. Life in its current form would not be possible at all without this protective screen.

But the ozone layer has got dangerously large holes. The reason for this are chemical substances that humans have blown into the atmosphere. The greatest enemy of ozone is chlorofluorocarbons, or CFCs for short. For a long time this gas was used as a coolant in refrigerators and as a propellant in spray cans. In itself odorless and non-toxic, CFCs are only dangerous to humans when they rise: in the stratosphere it reacts with ozone, thus attacking and destroying the ozone layer.

But if the UV radiation is no longer shielded by the ozone layer, then it damages life on this planet. We get sunburned much faster and have to use stronger and stronger sunscreens. In the worst case, skin cancer is the result of the unfiltered radiation. The eyes are also badly attacked; without the ozone layer we would go blind. The people in Australia and New Zealand are particularly affected, because the ozone hole is the largest near them - above the Antarctic. The ozone layer is also thin over the North Pole because the ozone is broken down more quickly in extreme cold.

If the UV light reaches the earth unhindered, another problem arises: unicellular plants die on the surface of the sea - the phytoplankton. However, this plankton is very important to us because it provides oxygen and uses up carbon dioxide in the process.

Fortunately, scientists have discovered the connection between CFCs and the ozone hole. Politicians also reacted just in time. The ozone killer CFC is now banned worldwide. The ozone layer is slowly recovering. However, it will take a few years before it is completely healed, because CFCs are very stable. It only degrades slowly and the gases are still on their way up. There they can still attack the ozone layer for over a hundred years.

A shell made of gas

Seen from space, it appears like a fine bluish veil that surrounds the earth: the atmosphere. It is the envelope of air that surrounds our planet. Compared to the diameter of the earth, this shell is quite thin: if the earth were the size of an apple, the atmosphere would be about the thickness of its shell.

Without the atmosphere there would be no life on this planet, because plants, animals and humans need air to breathe. It protects us from the cold and from harmful radiation from space. It also lets meteorites burn up before they can hit the surface of the earth. This atmosphere is vital to us - but what is it actually made of?

The atmosphere is a mix of different gases. A large part of this gas mixture is nitrogen: At 78 percent, that's almost four fifths of the entire atmosphere. Only 21 percent consists of oxygen, which we need to breathe. The remaining one percent is made up of various trace gases - gases that only occur in traces in the atmosphere. These trace gases include methane, nitrogen oxides and, above all, carbon dioxide, or CO for short2 called. Although the CO2-Proportion is quite low, this trace gas has a tremendous impact on our earth's climate. This can be seen in the greenhouse effect, which is heating up our planet.

The fact that the earth has an atmosphere at all is due to gravity. It holds the gas molecules on earth and prevents them from simply flying out into space. In fact, the air becomes thinner and thinner with increasing altitude and thus decreasing gravity. Even at 2000 meters above sea level, this can become uncomfortable for people: He suffers from altitude sickness with shortness of breath, headaches and nausea. Extreme mountaineers who want to climb high peaks like the 8000m high in the Himalayas therefore usually take artificial oxygen with them on their tour.