The atmosphere is a layer of gases surrounding the earth
- the troposphere
- 0-15km above sea level
- densest layer, contains the most gas molecules per unit volume
- the stratosphere
- 15-50km above sea level
- enriched in ozone molecules, which absorb harmful UV radiation from the sun
Greenhouse gases:
- trap and re-radiate solar radiation to the Earth, creating the greenhouse effect, which enables life on Earth
- too many greenhouse gases in the atmosphere, in too-high abundance, causes the enhanced greenhouse effect, which is caused by human activities
- what is the greenhouse effect?
- UV and visible radiation from the Sun warms up the Earth
- the Earth loses energy as infrared radiation
- greenhouse gases absorb infrared radiation and prevent it from escaping, so less heat energy is lost to space, making the Earth steadily warmer
- what makes a greenhouse gas?
- the molecule must have a polar bond, which can absorb infrared radiation
- eg. N2 and O2 have identical electronegativities, so their bonds are not polar - they are not greenhouse gases
- eg. CH4 and CO2 do have polar bonds, so are greenhouse gases
- water is the greatest contributor to the greenhouse effect
- CFCs may only be present in small concentrations, but they are very stable and take a long time to decompose
- cattle farming increases the concentration of methane in the atmosphere
- methane absorbs more IR per molecule than CO2
- air pollutants:
- CO2 produced by the combustion of fossil fuels
- SO2 produced when sulphur (naturally present in fossil fuels) combusts
- reacts with water in the atmosphere to form acid rain
- NOx formed when nitrogen and oxygen react together in the high temperatures of car engines
- can react with water in the atmosphere to form acid rain
- produces a photochemical smog, which reduces visibility and can cause respiratory illnesses
- CFCs, used to be widely used in refrigerants and aerosols
- react with and deplete the ozone layer, allowing harmful UV light to reach the Earth’s surface
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