E2 INFRARED (IR) SPECTROSCOPY Vivien Tsang and Melody Mak

WHAT IS THE GREENHOUSE EFFECT? The greenhouse effect is a natural process The atmosphere traps some of the energy that comes from the sun This energy provides warmth to support life on Earth However Due to an increase in human activity, there has been a significant rise in the concentration of greenhouse gases Scientists have observed that the rise in the level of carbon dioxide (a greenhouse gas) has caused a rise in global temperatures over the years This is called global warming

THE GREENHOUSE EFFECT & RADIATION Radiation from the sun reaches the Earth through short wavelength ultraviolet radiation and visible radiation These are either: 1) Reflected back into space 2) Absorbed by the atmosphere before reaching Earth’s surface Energy radiated from the Earth’s surface are longer wavelengths of infrared radiation but not all of it escapes back into space. This is because the greenhouse gases acts like a greenhouse, absorbing the radiated energy from the Earth's surface, which is then reradiated back down into the Earth.

SO HOW IS THE GREENHOUSE EFFECT CAUSED? Greenhouse gases: allow the passage of incoming short wavelength radiation (UV and visible radiation) Absorb some of the reflected longer wavelength radiation, so that these are radiated back to Earth’s surface Therefore greenhouse gases cause heat to be trapped as some of the long infrared radiation reflected from the Earth cannot escape.

THE GREENHOUSE EFFECT The relative effect of greenhouse gases on global warming depend on: - its concentration/abundance in the atmosphere - its ability to absorb infrared heat Water vapour is the main greenhouse gas because it is the most abundant and is always in the atmosphere CO 2 contributes about 50% to global warming Bonds in CO 2 absorb a different wavelength of radiation. Even though it only constitutes 0.03% of the atmosphere, it has a significant role in maintaining the average global temperature (around 15˚C)

THE GREENHOUSE GASES: SOURCES GasMain sourceHeat trapping effectiveness relative to CO 2 Overall contribution to global warming H2OH2OEvaporation of oceans and lakes CO 2 Combustion of fossil fuels and biomass 1 50% CH 4 Anaerobic decay of organic matter caused by intensive farming 30 18% N2ON2OArtificial fertilisers and combustion of biomass and hydrocarbons 150 6% O3O3 Secondary pollutant in photochemical smog % CFCsRefrigerants, propellants, foaming agents, solvents %

INFLUENCE ON GLOBAL WARMING Consequences: Changes in agriculture and biodistribution Rising sea levels due to thermal expansion and melting of the polar ice caps. This leads to: => increased flooding => oceans absorbing more heat => more hurricanes and typhoons Significant changes in world weather patterns Increased risk of diseases e.g. Malaria – mosquitoes spread to areas of warmer climate Economic problems as tourism pattern changes Problems of maintaining a sufficient supply of fresh drinking water

INFLUENCE OF PARTICULATES Particulates have the opposite effect to greenhouse gases They are able to lower the temperature by scattering short wavelength radiation so that it is reflected back into space Examples of particulates: soot, ash, volcanic dust