Atmospheric circulation systems operate on such a large scale that one is perhaps inclined to doubt that man’s activities would have any appreciable effect on them. However, it is known that the global heat balance has changed over the last few decades, and we might ask ourselves how much of this is a result of man polluting the atmosphere. The problem is not so much to establish that man has an impact on the atmosphere but to evaluate it in comparison with the natural forces of change.
Atmospheric changes introduced by man may be grouped into three categories: the introduction of solids and gases not normally found in the atmosphere (pollutants); changes in proportions of the natural component gases of the atmosphere; and alterations of the earth’s surface in such a way as to affect the atmosphere.
Pollutants in the Atmosphere
To city-dwellers the most obvious way in which man has affected the atmosphere is through pollution. Pollutants include particulate matter, both solid and liquid particles, and gaseous substances such as sulphur dioxide (SO2), oxides of nitrogen (NO, NO2, NO3), carbon monoxide (CO) and hydrocarbon compounds. But not all man-made pollution comes from cities. Isolated industrial activities frequently create a footprint of atmospheric pollution in areas of countryside downwind from the industrial site: particularly infamous examples in Britain include smelters and brickworks. Mining and quarrying activities also send large amounts of mineral dust into the air. Even man-induced forest and grass fires as well as bonfires, can greatly add to particulate pollution at certain times of year.
Atmospheric pollutants are conducted upward from the emission sources by rising air currents as part of the normal convective processes. Larger particles settle under gravity and return to the ground as fallout. Smaller suspended particles are brought to the Earth by precipitation as washout. By a combination of the two processes the atmosphere tends to be cleaned of pollutants, and in the long run a balance is achieved between the input and output of pollutants, although there are large fluctuations in the quantities stored in the air at a given time. Pollutants are also eliminated from the air over their source areas by winds which disperse the particles into large volumes of clean air in the downwind direction. Smoke stacks are intended to take as much advantage of this as possible. The passage of a cold front accompanied by strong winds is usually very effective in sweeping away pollutants from an urban area, but during stagnant anticyclonic conditions concentrations may rise to high values, sometimes producing smog.
Once in the atmosphere, the primary pollutants undergo a number of chemical reactions, generating a secondary group of pollutants. For example, sulphur dioxide (SO2) combines with oxygen and suspended water droplets to produce sulphuric acid. This acid is harmful to organic tissues and is also very corrosive. Photochemicalreactions are brought about by the action of sunlight: for example, sunlight acting on nitrogen oxides and organic compounds produces ozone (O3). Another toxic chemical produced by photochemical action is ethylene.
The harmful effects of atmospheric pollution on plant and animal life are manifold. For humans, many pollutants are irritant to the eyes and dangerous to the respiratory system. During the London smog of December 1962, more than 4,000 additional deaths occurred. Ozone in urban smog has a severe effect on plant tissues; atmospheric sulphuric acid has wiped out lichen growth in many urban areas of Britain. Lead and other toxic metal particles are a particular cause of concern for human health. In addition, pollution also causes many millions of pounds worth of damage to materials: limestone structures suffer greatly in certain British cities unless treated with preservatives.
The global effects of foreign particles in the atmosphere in altering radiation and heat balances is difficult to assess. There have always been major natural sources of particles in the atmosphere, including forest fires and large volcanic explosions. Careful monitoring by U.S. scientists of temperature trends and dust amounts at various heights in the atmosphere has led to the tentative conclusion that man’s contribution to atmospheric particles may have far-reaching effects on tropospheric processes – for example, on the rain-making mechanism – but perhaps little effect on processes in the stratosphere.
(Bryant, Richard H. Physical Geography Made Simple, Oxford, 1993)
7. You are going to read a magazine article about weather forecasting. Choose the most suitable heading from the list A-l for each part (1-7) of the article. There is one extra heading which you do not need to use. There is an example at the beginning (0) – I.
| A) Coming up with a forecast В) You can still have a go С) Do they always get it right? D) Small but powerful E) Useful information for the | F) Hi-tech assistance G) An art not a science H) Difficulties with long-term I) An opposing view |
WHAT’S GOING TO BE LIKE TOMORROW?
ANDY GRAY EXPLORES THE SCIENCE OF MODERN
WEATHER FORECASTING
0) The British like to talk about the weather, that’s what they say. True, but they particularly like to complain when the weatherman (or weather-woman) gets it wrong. Edward Lorenz, a scientist whose research led to the development of chaos theory in physical systems, has a different approach to weather forecasting. In The Essence of Chaos, he writes, ‘To the often heard question, ‘Why can’t we make better weather forecasts?’ I have been tempted to reply, ‘Well, why should we be able to make any forecasts at all?
1) What he is saying is that, in meteorology, one has to remember that a tiny difference in the initial conditions of the atmosphere can have an enormous effect on what the weather will be like several days later. For example, whether or not a butterfly flaps its wings in South America could be the difference between whether there’s a storm m Europe or not.
2) Some of these differences, like the proverbial butterfly above, are too small to detect. That’s why meteorologists will probably never be able to provide us with accurate day-to-day weather forecasts several weeks in advance. Today, the longest period of time they can forecast with some accuracy is five days. And even this is frequently not accurate enough for us to totally rely on.
3) So how do they forecast the weather? The first step is observation. Meteorologists all over the world are constantly taking readings, measurements and recordings of what the weather is like now. This information is collected, and fed into computers which use mathematical models to come up with predictions. There are different models, and each model will come up with a (slightly or enormously) different prediction.
4) The key question, of course, is ‘How accurate are these predictions?’ The answer is that it depends. Remember the butterfly we talked about above? Sometimes small differences in the initial conditions have a large effect on weather systems, but sometimes they don’t. In other words, sometimes the weather is more predictable than at other times. Because of this, forecasters run their computer models several times, and each time they change the initial conditions slightly. If the resulting predictions are all similar to each other, the forecast is more likely to be right.
5) Of course, the more advanced modern technology becomes, the better we are at forecasting the weather. These days, it’s not just a question of looking at the barometer and measuring wind speed to decide what the weather’s going to be like tomorrow. Weather forecasting is extremely complex, making use of radar and satellites and global communication systems. Also, the more powerful the computers that produce the models are, the more accurate the forecasts will be.
6) Does that mean that there’s no place for amateur weather forecasting anymore? Well, yes and no. Meteorologists say that relying on old weather proverbs such as ‘red sky at night, shepherds’ delight’ and ‘fair weather cometh out of the north’ are really not reliable. The problem is they were usually created a long time ago, often in different parts of the world. What may have been generally true then and there is not universally true today. However, watching the rise and fall of your barometer and checking the direction of the wind can prove a fairly reliable indicator of the weather to come.
7)
| wind direction | barometer reading | weather forecast |
| SW to NW | 30.10-30.20 (steady) | fair, with slight temperature changes for 1-2 days |
| SW to NW | 30.10-30.20 (rising rapidly rapidly) 30.10-30.20 (rising rapidly) | fair, followed by rain within 2 days days |
| S to SE | 30.10-30.20 | rain within 24 hrs (falling slowly) |
| going to W | 29.80 or below (rising rapidly) | clearing and getting colder |
8. Read the passage about the ozone layer and answer the questions (1-14) by writing a word or a short phrase. The first one is done for you as an example.
Model: 1. Where is ozone found? the Earth’s stratosphere
2. What does ozone filter out?
3. Where is there a high level of concentration of ozone?
4. What was London known as in the past?
5. What was the major cause of London’s smog?
6. What does sunlight encourage to turn into ozone?
7. Give two examples of crops affected by too much ultra-violet radiation.
8. What are malignant melanomas?
9. Give one of the two vital properties of CFCs.
10. About how long does it take СFСs to break down?
11. When does chlorine become an ozone destroyer?
12. What do the scientists compare with the area of the United States and the height of Mount Everest?
13. Do governments ban CFCs?
14. Is CFC a ‘greenhouse’ gas?
Ozone, spread thinly in the Earth’s stratosphere, about 10 km to 50km above ground level, is essential to all forms of life. The molecules of ozone at that level ‘filter out’ high energy ultraviolet (UV) radiation from the sun, and in doing so protect plants and animals from harmful UV rays. Many scientists believe that certain forms of life were unable to live on land before the ozone layer had formed. But, nearer the ground, ozone is a problem, and by the sea it may even damage your health. Scientists now believe that the invigorating effect that comes from being near the sea is not caused by ozone in the atmosphere, but instead is a result of ions (electrically charged particles) in the sea air. Similarly, the distinctive smell of the sea probably comes from old fish and rotting seaweed, rather than ozone. But even more serious than the effect of ozone by the sea is its high level of concentration in polluted cities all over the world.
In the past, London was so famous for its smogs that the city was commonly known as ‘the Smoke’. These smogs were thick, smoky fogs which enveloped the city, and they persisted until the early 1960s. Coal-burning fires were the major cause of this health hazard, which was not eradicated until legislation was enacted in the late 1950s, setting up ‘smokeless zones’ and controlling the types of fuel that could be burned. But recently, a new type of smog has hit the headlines – of which one of the constituent parts is ozone. The combination of exhaust gases from cars and factories, still air, warmth and clear sunshine, has resulted in a highly poisonous form of ozone. Sunlight encourages a chemical reaction which changes oxygen in the air to ozone – hence the name ‘photochemical smog’; even small amounts of ozone can irritate people’s eyes, give them headaches and affect their breathing. Higher concentrations can also damage plant tissues, and may have other, more severe, consequences. In short, ozone is best kept at a distance from plants and animals.
So when does ozone become a friend to life on earth? Well … the molecules of ozone ensure that a good deal of UV radiation is prevented from reaching people and plants on Earth (and within 10 km of the earth). This is good news for plants – because crops such as maize, wheat and rice give lower and poorer quality yields if too much UV radiation reaches them.
It is good news for human beings too – high levels of UV radiation can cause
malignant melanomas, or skin cancers, some of which may be capable of spreading to other parts of the body if they are not treated at an early stage. Why is it that ozone has become so well-known in the last decade? The answer involves ozone itself, UV radiation, and a family of chemicals called chlorofluorocarbons (or CFCs).
CFCs were first demonstrated by the American inventor Thomas Midgley when he inhaled a lungful of CFCs gas and used it to blow out a candle. This showed two vital properties of CFCs: they do not burn and they are not poisonous. For this reason they became the ideal replacement for ammonia in refrigerators: ammonia is toxic, inflammable, and has an unpleasant smell.
The CFC family of chemicals has many other uses, for example, inside aerosols. Within a can, the CFC is a liquid; when the pressure is released it becomes a gas. Other uses are as cleaning solvents.
In Thomas Midgley’s time, CFCs seemed the answer to many problems. Unfortunately, each time they are used some of the gas escapes into the atmosphere. CFCs are very stable – it takes perhaps 75 years before they break down. They remain in the air and reach high into the atmosphere.
This is where the problems begin. Up in the stratosphere, conditions seem to be perfect for breaking down CFCs and releasing chlorine. This is especially true during the cold winters above the South Pole in Antarctica. In temperatures of below –80°C, atoms of chlorine are formed. When the sun returns in spring, the chlorine becomes an ozone destroyer.
Just one chlorine atom can destroy thousands of ozone molecules.
The scientist Joe Farman, until recently head of the British Antarctic Survey team which has been carrying out research in the Antarctic for the past 20 years, first reported the ‘hole’ above Antarctica in 1985. Experts think that the hole is as big in area as the United States (approximately 9,500,000 sq km) and as deep as the height of Mount Everest (nearly 8,850 m). Every southern summer – early in November – the Antarctic hole breaks up into blobs of ozone-reduced air that drift around in the southern hemisphere.
Why do governments not just ban CFCs? The United States banned their use in aerosols five years ago, since when few countries have followed. Manufacturers have been working to find a replacement for CFCs which will not damage the ozone layer, and which does not have other harmful properties.
Some scientists believe that we should not have been so quick to condemn CFCs. They argue that gases from burning vegetation and wood-rotting fungi do far more damage to the ozone layer.
Even so, the effect of CFCs as a ‘greenhouse’ gas in warming the Earth is significant. The search to replace CFCs continues.
9. Read the text How Are People Affected by a Volcano Eruption? and answer the questions after it.