The presence of one or more contaminants in the air, that are injurious to humans, plants, animals and also to property is termed as air pollution.
Such harmful contaminants present in the air and causes pollution are called as air pollutants.
Sources of Air Pollution
There are two main sources of air pollution.
- Natural Sources
- Human Made Sources
- Natural radioactivity
- Wind blown dust
- Ozone layer
- Smoke and gases from fire.
- Gases and odour from natural decomposition
- Volcano gases and ashes
Human Made Sources
- Mobile Sources include all types of transportation sources such as, bus, truck and car etc.
- Stationary Sources include residential sources, industrial sources and electrical generation sources (Power Plant).
Classification of Air Pollution
Air pollution is classified on the basis of origin and state of matter.
Classification based on Origin
It is classified in two categories, primary and secondary.
In Primary, emitted to the atmosphere from a process and in Secondary, Formed in the atmosphere as a result of chemical reaction.
Classification based on State of Matter
It also categorize in two types.
- Gaseous pollutants
- Particulate pollutants
They are further classified as
- Inorganic gaseous pollutants
- Organic gaseous pollutants
Inorganic Gaseous Pollutants
Some major inorganic gaseous pollutants are as follows
- Sulphur gases like SO2, SO3 and H2S are mostly emitted from the rubber industries.
- Carbon gases like CO( engine emission) and CO2 is emitted by burning and decomposition.
- Nitrogen gases like NH3 and NOX are releasing from urea industry and engine emission.
- Halogen gases like HF is emitted from fertilizer industry.
- Cyanides like HCN is emitted from blast furnaces.
Organic gaseous pollutants
It includes hydrocarbons (like paraffins, aromatics and olefins) and aliphatic oxygenated compounds (like aldehydes, ketones and organic acid). The sources of organic gaseous pollutants are usually automobiles, petrochemical industries and service stations.
Control of Automobile sources pollution
The problem of air pollution becomes more serious due to the exhaust of automobiles and diesel driven vehicles, which contain large amount of harmful gases. Automobiles exit large quantities of both organic compounds and oxides of nitrogen, sulphur and carbon. They affect human beings and causes diseases of heart, lungs and respiratory system.
In order to control the automobile source pollution, the main approaches are:
- Engine design modification
- Fuel modification
- Exhaust gases treatment
- Exhaust gas circulation
Particles dispersed in a gaseous medium are collectively termed as aerosols and classified as dust, smoke, fumes, fog and mist, drizzle and rain.
Dust is produced by grinding, crushing and drilling etc. Particle size ranges from 1 μm – 200 μm.
Smoke is produced by burning of organic materials like wood and coal. particle size ranges from 0.01 μm – 1 μm.
Fumes are formed by process like sublimation and condensation. Particle size ranges from 0.01 μm – 1 μm.
Fog and Mist
It is formed by the condensation of water. Particle size ranges from 2 μm – 200 μm.
Drizzle and Rain
Droplets larger than 200 μm are termed as drizzle or rain.
it includes spores of fungi, pollens of microstructure and marine bacterias.
Effect Of Air Pollution
Humans, plants, animal and also materials are effecting by the air pollution.
Effect On Human Health
The major impacts of air pollution on the human health are:
- Eye, nose and throat irritation.
- Respiratory irritation due to dust.
- odour disturbance due to gases like H2S.
- Biological disorder due to radioactive fall out.
- Carcinogenic agents which causes cancer.
- Disease like asthma is caused by high concentration of SO2 and NO2.
Effect On Plants
Some major effects of air pollution on plants are:
- The air pollutants affects photosynthesis and thus retard the plants.
- The acute injury to plants occur to short term exposure to relatively high concentration.
- The chronic injury to plants is due to long term exposure. This leads to loss or reduction of chlorophyll resulting in discoloration of leaves and is called chloro-sis.
Effect On Animals
- Cattle sheep get poisoned from fluorine which originates from industries.
- They also get poisoned by lead and arsenic when plants are sprayed with insecticides.
- Common diseases in pet animals due to air pollution are asthma and bronchitis.
Effect On Materials
Air pollution affects material in following ways.
- Deposition and removal
- Chemical attack and corrosion
Thus air pollution is responsible for economic losses because of damages of material.