iii. Use of candles should be minimized.
iv. Gas emissions from industries are controlled using wet scrubbers. These have a convergent inlet that is used to pass water and air at high velocities to remove the dust particles.
v. Catalytic converters should be used in vehicles to control vehicular pollution. Catalytic converter consists of platinum and palladium metal catalysts which convert the more harmful gases into less harmful ones, for example carbon monoxide is oxidized to carbon dioxide.
vi. Dust particles can be separated from air using gravitational settling chambers. Gravitational setting chambers are pre-cleaners that remove larger particles from the air. These gravity chambers are often used by metal industries to collect large particles. The velocity of gas is reduced in these chambers to separate dust from gas. The solid particles settle due to gravity in the rectangular chamber of the device.
vii. Cyclone dust collectors are universal air pollution controllers that can be used at home as well as in industries. They are funnel-shaped metal tubes where debris is sucked in at the top.
viii. To remove particulate matter from the gas stream, filters are used. The filters can be made of fibrous material like cloth, granular material like sand and mat. In industries, most common system is bag house system.
For low temperatures, bag is made up of cotton/synthetic fibres and for high temperatures glass cloth fabrics are used. Bags need to be cleaned periodically either through mechanical shaking or by reverse air jets or reverse flow of gas through the bags.
ix. Electrostatic precipitators or ESPs are used to collect particles from the air. An electronic charge is used to remove particles from flowing gas. ESPs can remove fine particulates like dust and smoke. World over particulate matters are removed using ESPs. ESPs charges dust with ions and collect ionized matter on an oppositely charged surface. It can work in very high temperatures as in boilers in thermal power plants, steel plants and cement factories.
x. Scrubbers are wet collectors and remove aerosols from a stream of gas either by collecting wet particles on a surface or the particles are wetted by a scrubbing liquid or water and particles are then trapped from the passing gases.
Dry scrubber or gravel bed filters are used for prefilteration of gas before actual filtering operation. This is a good system of removing fly- ash from hot stream of gases.