Measurement of Gaseous Emissions

When a gas containing sulphur dioxide is irradiated using ultraviolet light of appropriate wavelength, sulphur dioxide molecules are excited to an energy level higher than the original. When returning to the normal lower energy level, excited molecules give up their extra energy, giving rise to another radiation called fluorescent radiation (also in the ultraviolet wavelength range), the intensity of which is detected. This principle is generally used for the measurement of the concentration of sulphur dioxide in emission gases