Introduction of chemicals, particulate matter, biological materials which cause harm or discomfort to humans or other living organisms, and cause damage to the natural environment is Air Pollution. The Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to the Earth’s ecosystems. Some of the air pollutants such as carbon dioxide, methane and water vapor absorb the long wave radiation and prevent much of it from passing out and away from the earth. They create a blanket around the earth and therefore keep the air and the ground warmer than it would otherwise be. The effect is known as Green House Effect. The Gases which cause this effect are called GHGs (Green House Gases). Green House Effect has led to the Global Warming.
The Air Pollutants can be solid particles, liquid droplets, or gases. They can be natural or manmade. The pollutants have been classified into primary and secondary categories.
- The primary pollutants are “directly” emitted from the processes such as fossil fuel consumption, Volcanic eruption and factories.
- The secondary pollutants are not emitted directly. The secondary pollutants form when the primary pollutants react with themselves or other components of the atmosphere.
Primary Air pollutants
The major primary pollutants are Sulfur oxides, Nitrogen Oxides, Carbon dioxide, particulate matter, Methane, Ammonia, Chlorofluorocarbons, Toxic metals etc.
- The Sulfur Oxides are generally a product of the Volcanoes, Industrial processes, Coal and petroleum, because most of them have Sulfur as a component. The Sulfur Dioxide in presence of a catalyst such as NO2 causes Acid Rain, because of the formation of Sulphuric Acid.
- Most of the Nitrogen Oxides are produced due to high temperature combustion. In the cities the brown haze dome above the cities is mostly because of the Nitrogen Oxides. The most important toxic gas is Nitrogen dioxide which is brown, with sharp odor.
- Carbon Monoxide, which is colorless, odorless and non irritating but very poisonous gas is the product of incomplete combustion of the natural gas, coal or wood. The vehicle exhaust is the major source of CO.
- The Carbon Dioxide is associated with the Ocean Acidification and is emitted from combustion, factories and respiration of living organisms.
- Then, we have primary pollutants such as Volatile Organic Compounds or VOCs which are methane (CH4) and non-methane (NMVOCs).
- Methane is a GHG which contributes to Global Warming.
- The NMVOCs include the aromatic compounds such as benzene, Toluene, Xylene which are proved and suspected carcinogens. Another dangerous compound is the 1,3-butadiene, often associated with industrial uses.
- The particulate matters are the fine particles which may be either solid or liquid, suspended in a gas. They are different from the Aerosols. Aerosols are particle and gas referred together.
- The aerosols which are created by the Human activities are anthropogenic aerosols. They account for around 10% of the total aerosols in the atmosphere.
- Then we have toxic metals as primary pollutants such as Cadmium, Lead and Copper, which are products of the Industrial processes.
- The Chlorofluorocarbons (CFCs) are proved to be harmful to the ozone layer emitted from products currently banned from use.
- In agriculture process, Ammonia is emitted which has characteristic pungent odor. It is a precursor to foodstuffs and fertilizers. Ammonia is also a building block for the synthesis of many pharmaceuticals.
Secondary Air Pollutants
Most important secondary level Air Pollutants are Ground Level Ozone, Smog and POPs . They are discussed in brief in the following pages.
Deaths due to Air Pollution
- As per the WHO estimates, around 24 Lakh people in the world die due to direct impact of the air pollution. Out of which 15 Lakh people die due to Indoor pollution, due to the cardiopulmonary disease linked to breathing fine particle air pollution.
- The Air pollution has caused several short term disasters.
- In 1984, the Bhopal Disaster was caused on December 2-3, 1984, due to a leak of methyl isocyanate gas and other chemicals from the plant resulted in the exposure of hundreds of thousands of people. It killed more than 25,000 people outright and injured 150,000 to 600,000 people.
- Similarly in 1952, in UK , the Great Smog of 1952 was formed over London on December 4. It was in the cold weather, combined with an anticyclone and windless conditions that the collected airborne pollutants mostly from the use of coal formed a form a thick layer of smog over the city. In six days more than 4,000 died, and 8,000 more died within the following months.
- In 1979, there was an accidental leak of anthrax spores from a biological warfare laboratory in the USSR near Sverdlovsk caused death of many people.