Discuss in brief the following:
(a) Green house gases
(b) Catalytic converter
(c) Ultraviolet B
(a) Green house gases: The gases which are transparent to solar radiation but retain and partially reflect back long wave heat radiations are called greenhouse gases. Green house gases are essential for keeping the earth warm and hospitable. They are also called radiatively active gases. They prevent a substantial part of long wave radiations emitted by earth to escape into space. Rather green house gases radiate a part of this energy back to the earth. The phenomenon is called greenhouse flux. Because of greenhouse flux, the mean annual temperature of the earth is 15°C. In its absence, it will fall to -18°C.
However, recently the concentration of greenhouse gases has started rising to result in an enhanced greenhouse effect that is resulting in increasing the mean global temperature. It is called global warming. A regular assessment of the abundance of greenhouse gases and their impact on the global environment is being made by IPCC (Intergovernmental Panel on Climate Change). The various green house gases are CO2 (warming effect 60%), CH4 (effect 20%), chlorofluorocarbons or CFCs (14%) and T nitrous oxide (N2O, 6%). Others of minor significance are water vapors and ozone.
(b) Catalytic converter: Catalytic converters are devices that are fitted into automobiles for reducing the emission of gases. These have expensive metals (platinum – palladium, and rhodium) as catalysts. As the exhaust passes through the catalytic converters, unburnt hydrocarbons are converted into CO2 and H2O and carbon monoxide and nitric oxide are changed to CO2 and N2 respectively. Vehicles fitted with catalytic converters should be run on unleaded petrol as leaded petrol would inactivate the catalyst in the converters.
(c) Ultraviolet B: UV-B having 280-320nm wavelength. Their harmful radiations penetrate through the ozone hole to strike the earth.
On earth, these can affect human beings and other animals by causing:
- Skin cancer
- Blindness and increased incidence of cataract in eyes, and
- Malfunctioning of the immune system.
- Higher number of mutations.