7.1.1.1. Types of air pollutants

Pollutants may be classified according to origin and state of matter.

According to Origin:

Air pollutants are divided into two categories as primary & secondary.

1. Primary air pollutants are those which are emitted directly into the atmosphere. Eg: C; CO; CO; SOx; N; S; H; NOx; CFC’s etc.
2. Secondary air pollutants are those which are produced in the air by the interaction among the primary air pollutants or by reaction with atmospheric constituents. Eg: Ozone (O3); Smog; Para Acetyl Nitrate (PAN); Acid Rain; Aerosols.

Air pollutants are divided into primary and secondary by their origin. Primary pollutants are released directly into the air from sources like vehicles, industries, or natural processes. For example, carbon monoxide (CO) from car exhaust is a primary pollutant. Secondary pollutants, on the other hand, form in the atmosphere when primary pollutants react with each other or with atmospheric components. Ozone in the lower atmosphere is a classic example of a secondary pollutant because it is created from the interaction of sunlight with other pollutants like nitrogen oxides.

Think of primary pollutants like raw ingredients in cooking; they are the basic components you use directly. For instance, the smoke from a chimney represents primary pollution. In contrast, secondary pollutants are like a finished dish that you create by cooking those ingredients together, such as the smog that forms when sunlight interacts with vehicle emissions.

According to State of Matter:

Air pollutants include fine solids, liquids, and gases. Dust, Smoke, Fumes etc are examples for solid particles whereas fog is an example for liquid particles.

Air pollutants can also be categorized based on their physical state. Solid pollutants include dust and smoke, which can settle on surfaces and affect air quality. Liquid pollutants often appear in the form of droplets, like fog or fine mists, that can carry harmful substances. Gaseous pollutants, such as carbon dioxide (CO2) or sulfur dioxide (SO2), are invisible but can be harmful to health and the environment.

Imagine a sponge soaking up water—moisture in the air is like the liquid pollutants, while the sponge itself represents solid pollutants that can accumulate and cause issues. When discarding old sponges (solid pollutants), or when water evaporates, we need to consider how they affect our space, similar to how air pollutants affect the environment.

PRIMARY POLLUTANTS

1. Carbon Monoxide: It is a colorless, odorless, poisonous gas that is produced by the incomplete burning of carbon based fuels (coal, petrol, diesel, and wood) which comes from the automobile industries, exhaust devices. About 70% of CO emissions are from the transport sector. When the air is polluted with CO, human blood is likely to be deprived of oxygen and leads to coma and death. In mild dosages, it leads to headache.

2. Oxides of Sulphur: SO2 is a gas produced from burning of coal, mainly in thermal power plants. It is injurious not only to humans and plants, but it also attacks rapidly a few rocks such as limestone, marbles, electric contacts etc. It can even dissolve nylon. SO2 polluted air leads to corrosion of metals. SO3 is more irritant than SO2 because it combines immediately with water to form sulphuric acid.

3. Oxides of Nitrogen: Combustion of fuels produces up to 50 ppm of Nitrogen oxides. High levels of NOx exposure can cause respiratory infections. They also contribute to the formation of ozone and acid rain.

4. Chloro Fluoro Carbons: CFCs are non-toxic and used as coolants in air conditioners. They are the main cause of ozone depletion and have a long lifetime in the atmosphere.

Primary air pollutants are those that are directly emitted into the atmosphere without any transformation. Carbon monoxide is a major pollutant from vehicles that can cause serious health effects like headaches or even death at higher concentrations. Oxides of sulfur and nitrogen result from burning fossil fuels. These gases not only harm human health but also contribute to environmental issues like acid rain and ozone depletion due to their chemical reactions in the atmosphere.

Consider a busy road where cars and trucks are continuously passing by. The exhaust from these vehicles is like smoke from a fire—it creates visible pollution. Just as smoke can fill a room and make it hard to breathe, these primary pollutants enter the air and can have detrimental effects on our health and the planet.

SECONDARY POLLUTANTS:

1. Ozone (O3): This is formed when oxygen interacts with other pollutants in sunlight. Ozone protects against UV radiation, but at ground level, it can cause health problems like respiratory issues.
2. Smog: A mixture of smoke and fog, smog can lead to respiratory problems and other health issues.
3. Acid rain: Resulting from SOx and NOx combining with atmospheric water vapor, acid rain can harm ecosystems and structures.

Secondary pollutants are not directly emitted but are formed through chemical reactions in the atmosphere. Ozone, while beneficial in the upper atmosphere, becomes harmful at ground level where it can cause health problems. Smog, a combination of fog and smoke, can reduce visibility and impact lung health. Acid rain, caused by sulfur and nitrogen oxides combining with moisture, can severely damage plant life, aquatic ecosystems, and buildings.

Think of secondary pollutants like a recipe—just as ingredients combine to create something new, primary pollutants interact in the atmosphere to form secondary ones. For instance, if you bake cookies, the heat transforms the ingredients into something delicious. Similarly, pollutants interact with sunlight and moisture to create harmful effects like smog and acid rain.

--