Polluting the atmosphere

• Human activities are causing global warming.
• Combustion of fuel produces many pollutants.
• Humans can reduce their impact on the environment.
• The greenhouse effect is the retention of heat in the atmosphere caused by the build-up of greenhouse gases.
• The important gases in the atmosphere are nitrogen, oxygen and carbon dioxide.
• Without greenhouse gases, the Earth would be about 18°C colder on average than it is now.
• Greenhouse gases present in the atmosphere include water vapour, carbon dioxide, methane, nitrous oxide and CFCs (chlorofluorocarbons).
• Vapour is a cloud of liquid particles, and steam is water vapour.
• Carbon dioxide is a gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis.
• Methane is a colourless gas that can do harm to life forms.
• The greenhouse effect works by absorbing heat radiated from the Earth, then releasing energy.
• The capacity of a system to do work or the quantity required for mechanical work to take place is measured in joules (J).
• The greenhouse effect keeps the Earth warm by absorbing and re-radiating energy from the sun.
• Electromagnetic radiation at most wavelengths passes through the Earth's atmosphere, the Earth absorbs most of the radiation and warms up, then radiates energy as infrared radiation.
• Some of the infrared radiation goes into space, some of the infrared radiation is absorbed by greenhouse gases in the atmosphere, warming up the lower atmosphere.
• Human activities contribute to global warming by releasing greenhouse gases into the atmosphere.
• The greenhouse effect is a natural process, but human activities have accelerated it.