Definition Types Sources Effects and Control of Atmospheric Pollutants
The surface of the Earth is surrounded by an atmosphere which has different thicknesses at different heights. There are different layers that constitute the atmosphere and each layer has a different density. The troposphere is the lowest layer of the atmosphere in which all the organisms live. It is extended around 10 km above the height of the mean sea level. Troposphere consists of air, clouds and water vapours. The next layer in the atmosphere is the stratosphere which tends to extend from roughly 10 to 50 km above the troposphere. It consists of the dioxygen, dinitrogen, and the ozone layer. The ozone layer is the one that tends to protect both humans and animals from the harmful UV rays of the sun. The pollution in these atmospheric layers refers to atmospheric pollution. It is caused by air or atmospheric pollutants and is known as the pollution of both troposphere and stratosphere.
Today, in this article, you will all the notes for atmospheric pollution class 11 which includes what are the types of pollution including tropospheric pollution and the stratospheric pollution.
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Tropospheric Pollution
Tropospheric pollution is caused due to the presence of unwanted gaseous or solid components in the air. These pollutants are classified as follows:
1. Gaseous Pollutants: The oxides of nitrogen and sulphur, ozone, hydrocarbons, and several other oxidants tend to fall under this category. Let us learn more about these atmospheric pollutants in detail.
a. Oxides of Sulphur: When we burn fossil fuel, the oxides of sulphur get produced. Sulphur dioxide is highly poisonous. Several studies show us that even a very low concentration of the gaseous sulphur dioxide tends to cause many respiratory diseases. Sulphur dioxide gets oxidized and changes to sulphur trioxide in the presence of the particulate matter.
2SO2 (g) + O2 (g) → 2SO3 (g)
b. Hydrocarbons: Hydrocarbons tend to get formed through the incomplete combustion of the fuels. They are carcinogenic, which means that they tend to cause cancer. They are also very harmful to the plants since they tend to cause ageing, shedding of leaves, and the breakdown of tissues.
2. Particulate Matter: Minute liquid droplets or solid particles that are suspended in the air are referred to as particulate matter. There are basically two different kinds of particulate matter which are viable and non-viable. The microorganisms like fungi and bacteria that are dispersed in the atmosphere are referred to as the viable particulates. The non-viable particulate matter is the one that is classified depending on the nature and size of the particles. Say, for example, smoke contains both solid and liquid particles that tend to get formed when the organic matter is combusted. Whereas, on the other hand, dust consists of fine particles that get produced when it is ground or crushed.
Stratospheric Pollution
The stratosphere layer of the atmosphere consists of the ozone layer that saves our planet from the harmful UV rays of the sun. UV radiation tends to split the dioxygen molecule into the free oxygen atom. These free oxygen atoms tend to combine with the dioxygen molecule and form ozone.
O2- → uv O(g) + O(g)
O(g) + O2(g) O3(g)
Ozone is unstable and tends to break down to the oxygen molecule. Chlorofluorocarbons are the primary reason for ozone depletion. They tend to react with the ozone which tends to form the oxygen molecule and chlorine monoxide radical. CFCs are the primary agents that produce the chlorine radicals in the layer of the stratosphere and tend to deplete the ozone layer. This depletion of the ozone layer is a serious threat to all the living organisms since ozone protects all the living organisms from the harmful sun rays that tend to cause skin cancer.
FAQs on Atmospheric Pollutants in Chemistry and Environmental Science
1. What are atmospheric pollutants?
Atmospheric pollutants are harmful chemical substances present in the air at concentrations that can damage human health, ecosystems, or materials. They may be:
- Primary pollutants: emitted directly (e.g., CO, SO2, NO, particulate matter).
- Secondary pollutants: formed by chemical reactions in the atmosphere (e.g., O3, HNO3, H2SO4).
These air pollutants arise from combustion, industrial processes, vehicles, and natural sources like volcanoes and forest fires.
2. What are the main types of atmospheric pollutants?
The main types of atmospheric pollutants include gaseous pollutants, particulate matter, and secondary photochemical pollutants. They are commonly classified as:
- Carbon compounds: CO, CO2
- Sulphur compounds: SO2, SO3
- Nitrogen oxides (NOx): NO, NO2
- Hydrocarbons (VOCs): methane (CH4), benzene
- Particulate matter (PM10, PM2.5): dust, smoke, soot
- Secondary pollutants: O3, peroxyacetyl nitrate (PAN)
This classification is widely used in air pollution chemistry and environmental monitoring.
3. What is the difference between primary and secondary pollutants?
The key difference is that primary pollutants are emitted directly into the atmosphere, while secondary pollutants are formed by chemical reactions in air. For example:
- Primary pollutant: SO2(g) released from coal combustion.
- Secondary pollutant: H2SO4(aq) formed via oxidation: 2SO2(g) + O2(g) → 2SO3(g), followed by SO3(g) + H2O(l) → H2SO4(aq).
Secondary pollutants are common in photochemical smog and acid rain formation.
4. How is carbon monoxide (CO) formed in the atmosphere?
Carbon monoxide is formed mainly by incomplete combustion of carbon-containing fuels due to limited oxygen supply. The typical reaction is:
- 2C(s) + O2(g) → 2CO(g)
In contrast, complete combustion produces CO2: C(s) + O2(g) → CO2(g). CO is toxic because it binds strongly to hemoglobin, reducing oxygen transport in blood.
5. How are nitrogen oxides (NOx) formed in air?
Nitrogen oxides (NO and NO2) are formed at high temperatures when nitrogen and oxygen react during combustion. The main reactions are:
- N2(g) + O2(g) → 2NO(g)
- 2NO(g) + O2(g) → 2NO2(g)
These reactions occur in vehicle engines and power plants and contribute to smog and acid rain chemistry.
6. What causes acid rain in atmospheric chemistry?
Acid rain is caused by the formation of sulphuric acid (H2SO4) and nitric acid (HNO3) from SO2 and NOx in the atmosphere. Key reactions include:
- 2SO2(g) + O2(g) → 2SO3(g)
- SO3(g) + H2O(l) → H2SO4(aq)
- NO2 reacts with water and oxygen to form HNO3.
These acids dissolve in rainwater, lowering its pH below the natural value of about 5.6.
7. What is photochemical smog and how is it formed?
Photochemical smog is a type of air pollution formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in sunlight to produce ozone and other oxidants. A key step is:
- 2NO2(g) → 2NO(g) + O2(g) (in sunlight)
- The oxygen atoms formed generate O3(g).
This leads to accumulation of O3, peroxyacetyl nitrate (PAN), and aldehydes, especially in urban areas with heavy traffic.
8. What is particulate matter (PM) in air pollution?
Particulate matter (PM) consists of tiny solid or liquid particles suspended in the atmosphere, such as dust, soot, smoke, and aerosols. It is classified by size:
- PM10: particles ≤ 10 μm
- PM2.5: particles ≤ 2.5 μm
Smaller particles penetrate deeper into the respiratory system and are a major concern in environmental chemistry and public health.
9. How do atmospheric pollutants affect the ozone layer?
Certain atmospheric pollutants like chlorofluorocarbons (CFCs) release chlorine radicals that catalytically destroy ozone in the stratosphere. A simplified mechanism is:
- Cl· + O3 → ClO· + O2
- ClO· + O → Cl· + O2
Overall reaction: O3 + O → 2O2. One chlorine radical can destroy many ozone molecules, leading to ozone depletion.
10. How can atmospheric pollution be controlled chemically?
Atmospheric pollution can be controlled using catalytic converters, scrubbers, and cleaner fuels to reduce harmful emissions. Key chemical methods include:
- Catalytic converters: convert CO and NOx into CO2 and N2.
- Scrubbers: remove SO2 by reacting it with CaCO3: SO2(g) + CaCO3(s) → CaSO3(s) + CO2(g).
- Use of low-sulphur fuels and renewable energy sources.
These strategies are central to environmental chemistry and air quality management.
