Major Air Pollutants:
The major air pollutants fall into six main categories of air pollutants:
- Aerosols and VOCs
- Oxides of carbon
- Other Hydrocarbons
- Sulphur Dioxide
- Particulate Matter
- Oxides of Nitrogen
Aerosols:
Aerosols are tiny particles suspended in the air. It is produced when solid or liquid dispenses in the air.
Example: Smoke, oceanic haze, smog. On average, globally, aerosols from human activities contribute about 10 percent of the total amount of atmospheric aerosols. Most of this is concerned in the Northern Hemisphere, due to industrial development, slash and burn in croplands, and overgrazed grasslands.
Natural aerosols in the air also arise from volcanoes, dust storms, forest fires, foliage, and sea spray. Nonetheless, harmless aerosols are created by the particles of carbon. Anthropogenic activities, such as fossil fuel burning and the change of natural surface cover also create aerosols.
VOCs:
The term VOCs refers to the class of organic chemical compounds with considerable vapor pressure. There are various types of VOCs present ubiquitously that can affect environmental and human well-being. VOCs include both natural and man-made chemical compounds.
It is the man-made VOCs that are controlled, especially for indoor environments where concentrations can be maximum. Commonly VOCs are used in household products like paints, paint strippers and other solvents, wood preservatives, aerosol sprays, cleaners and disinfectants, moth repellents, air fresheners stored fuels, automotive products, and dry-cleaned clothing.
POPs:
POPs are a toxic organic class of compounds that harmfully affect both the health and the environment throughout the world and have become a global concern. As they can be easily carried by currents of wind and water. Most of the POPs produced in one country affect man and nature far-off from the place they are used and released.
POPs including some pesticides and heavy metals evaporate from the soil in equatorial and tropical countries. Travel in the air towards comparatively cooler regions, where they condense with the falling of temperature. The processes repeat in ‘hops’ and are thus carried across thousands of km away within a few days. The more the volatility, the far they are carried and retained in the air. Such a mechanism of long-range atmosphere transport and subsequent deposition of POPs is called ‘grasshopper or global distillation process‘.
The process goes on and on with the highest concentrations in the circumpolar nations. In view of this, the Arctic Council was constituted by Denmark and Sweden. Iceland, Norway, Russia, Alaska, Greenland, Finland, etc, to monitor and assess the source and pathway.
Particulate Matter:
Particulate Matter (PM) or fine particles is a generic term used to represent a subdivision of solid particles or liquid droplets suspended in a gas or liquid. It is a complex mixture of airborne particles. They differ in origin, size, and chemical composition, all of which are < 10 µm in size.
They can be inorganic components like nitrates, sulfates, metals, carbon particles, or organic compounds like aerosols, POPs, etc. These fine particles are dispersed in air and can freely move over great distances. Most of the particles come from burning in fireplaces and wood stoves, automobile exhaust, etc.
i. Aldrin - Pesticide, closely related to dieldrin extensively used on corn and cotton and for termite control.
ii. Dieldrin - Pesticide widely used on corn and cotton pests. It is also a metabolite of aldrin.
iii. Chloridane - Pesticide on crops, lawns, and gardens and fumigant for terminate control.
iv. Heptachlor - Insecticide for household and agricultural uses. It is also a component and a breakdown product of chlordane.
v. DDT - Pesticide used for controlling malaria since Second World War was discovered by Paul Mueller.
vi. Endrin - It is used as an insecticide, rodenticide, and also to control birds.
vii. Hexachlorobenzene (HCB) - It is used as a pesticide and fungicide used on seeds is also an industrial by-product.
viii. Mirex - It used as insecticide and as flame retardant.
ix. Toxaphene - Insecticide used on cotton pests.
x. PCBs - It stands for Polychlorinated biphenyls widely used in electrical equipment.
xi. Polychlorinated Dioxins
xii. Polychlorinated Furans - Two notorious classes of unintentional pollutants, produced as byproducts of incineration and industrial processes.
CFCs:
CFCs are organic compounds comprising carbon, chlorine, and fluorine, produced as a capricious derivative of methane and ethane and commonly known as freons. A subclass of the CFCs is the hydrochlorofluorocarbons (HCFCs) which include hydrogen in addition commonly they are identified by the DuPont trade name freon. One of the most recognizable examples is Dichlorodifluoromethane (R-12 or Freon-12).
CFCs had been extensively used as refrigerants, propellants, and solvents. The production of CFC compounds is being phased out by the negotiation of the Montreal protocol since these add to the diminution of ozone in the stratosphere. Presently, gases such as helium, and propane/isobutane mixtures are used as refrigerants.