Air pollution

Air pollution is the biggest problem in larde cities and industrial areas. Emissions such as smoke, dust, smells and car and lorry exhausts may cause huge problems.
Trees are vitally important for our life because they are lungs of our planet. They absorb carbon dioxide from the air and gives out oxygen in return. But they are threatened both by pollution and by people.
• Smoke from power plants contains sulphur dioxide, carbon dioxide and nitrogen oxide which are produced by coal-fired power plants and industrial plants burning fossil fuels. Substances such as sulphur dioxide and nitrogen oxide mix with water vapour in the atmosphere and form sulphuric acid and nitric acid. Sunlight turns them into poisonous oxidants and they fall onto trees in the form of acid rain or snow and these trees are gradually killed by them.
• In some parts of the Earth, esp.in Asia and South America, trees are not threatened by pollution but by people. The great rain forests are being destroyed for firewood and for building material. The Amazon rain covers the area as large as the whole of Europe, contains about one third of the world's trees and provides about 50% of the world's annual production of oxygen. If we lose tropical forests, it will be difficult or even impossible to breathe. If there's more carbon dioxide in the air, the temperature will rise and it will cause melting of the ice-caps at the North and South Poles. As a result, the sea level will rise and many coastal areas (including big cities) will be flooded.

Another problem is greenhouse effect. Actually, there could be no life on Earth without it because the Earth is warmed up naturally by the atmosphere which also traps solar radiation. But emissions such as
• carbon dioxide (produced by burning fossil fuels),
• nitrogen oxides (from car exhausts),
• CFCs (chlorofluorocarbons from aerosol and refrigerators),
• methane ( a byproduct of agriculture from rice, cattle and sheep),
• vater vapour
prevent the heat from escaping. The result is the rise in the Earth's temperature, the melting of arctic ice and flooding of areas situated near sea level.

Another pollutant is ozone. But there're two kinds of ozone:
• ozone at lower atmospheric levels can contribute to greenhouse effect, especially in summer. It's produced by reaction of sunlight on car fumes. It can cause
• health problems (asthma attacs),
• corosion of certain materials,
• stunted growth of plants which results in lower yields of some crops.
• the layer in the upper atmosphere protects life against ultraviolet rays which cause skin cancer. But there's a hole in it, especially over Antarctica, caused in part by CFCs.