Air from earth's atmosphere contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and traces of hydrogen, helium, and other "noble" gases (by volume), but generally a variable amount of water vapour is also present, on average about 1% at sea level.
Effects of air pollution - definition
Respiratory and heart problems, global warming, acid rain and depletion of ozone layer.
Natural sources of air pollution - definition
Natural sources of sulphur dioxide include release from volcanoes, biological decay and forest fires. Natural sources of nitrogen oxides include volcanoes, oceans, biological decay and lightning strikes. Ozone is a secondary photochemical pollutant formed near ground level as a result of chemical reactions taking place in sunlight.
Man-made sources of air pollution - definition
Man is responsible for most of the world's air pollution, both indoors and outdoors. Everything from smoking a cigarette to burning fossil fuels tarnishes the air we breathe and potentially causes health problems as minor as a headache to as harmful as respiratory, lung and heart disease.