How Do Atmospheric Pollutants Affect Human Health and the Environment?
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: Types, Sources, and Effects
1. What are atmospheric pollutants as defined in environmental chemistry?
Atmospheric pollutants are substances present in the air in concentrations greater than their natural abundance, which produce a harmful effect on humans, animals, plants, or the environment. These can originate from both natural sources, like volcanic eruptions, and anthropogenic (human-made) sources, such as industrial emissions and vehicle exhaust. They are broadly classified as primary pollutants (emitted directly into the atmosphere) and secondary pollutants (formed in the atmosphere through chemical reactions).
2. What are the major types of atmospheric pollutants according to the NCERT syllabus?
As per the Class 11 NCERT syllabus, atmospheric pollutants are mainly categorised into two types based on their physical state:
- Gaseous Air Pollutants: These include oxides of sulphur (SO₂, SO₃), oxides of nitrogen (NO, NO₂), oxides of carbon (CO, CO₂), hydrocarbons, ozone, and other oxidants.
- Particulate Pollutants: These are minute solid particles or liquid droplets suspended in the air. Examples include dust, mist, fumes, smoke, and smog. Particulates are further classified as viable (e.g., bacteria, fungi) and non-viable (e.g., soot, asbestos dust).
3. How is tropospheric pollution different from stratospheric pollution?
Tropospheric and stratospheric pollution occur in different layers of the atmosphere and have distinct causes and effects:
- Tropospheric Pollution: This occurs in the lowest layer of the atmosphere (0-10 km altitude) where we live. It is caused by pollutants like SO₂, NOx, CO, and particulates. Its primary effects include the formation of acid rain, photochemical smog, and direct respiratory health problems for living beings.
- Stratospheric Pollution: This occurs in the layer above the troposphere (10-50 km altitude). The main concern here is the depletion of the protective ozone layer, primarily caused by chemical compounds like Chlorofluorocarbons (CFCs). The harm is indirect, as a thinner ozone layer allows harmful UV radiation to reach Earth's surface.
4. What is the difference between classical smog and photochemical smog?
Classical and photochemical smog are two distinct types of air pollution with different compositions and formation conditions:
- Classical Smog: Also known as London smog, it forms in cool, humid climates. It is a mixture of smoke, fog, and sulphur dioxide, making it reducing in nature.
- Photochemical Smog: This type of smog forms in warm, dry, and sunny climates. It results from the action of sunlight on nitrogen oxides and hydrocarbons from automobile and factory emissions. It is oxidising in nature and contains high concentrations of oxidants like ozone and Peroxyacetyl Nitrate (PAN).
5. What are the specific health effects of major atmospheric pollutants on humans?
Different atmospheric pollutants have specific adverse effects on human health:
- Carbon Monoxide (CO): Highly poisonous as it binds to haemoglobin, reducing the blood's oxygen-carrying capacity. High exposure can lead to headaches, impaired vision, and even death.
- Sulphur Dioxide (SO₂): Causes respiratory issues like asthma, bronchitis, and emphysema. It also causes severe irritation to the eyes.
- Oxides of Nitrogen (NOx): High concentrations of NO₂ can damage the lungs and lead to acute respiratory diseases in children.
- Particulate Matter (PM 2.5): Fine particulates can penetrate deep into the lungs, causing respiratory and cardiovascular problems.
6. How does acid rain form and what are its environmental consequences?
Acid rain is a significant environmental problem caused by atmospheric pollution. It forms when oxides of sulphur (SOx) and nitrogen (NOx) react with atmospheric water vapour to produce sulfuric acid (H₂SO₄) and nitric acid (HNO₃). This acidic precipitation has severe consequences, including:
- Damaging historical monuments and buildings, especially those made of marble (calcium carbonate).
- Making lakes and rivers too acidic for aquatic life to survive.
- Harming forests by damaging leaves and soil nutrients.
- Leaching heavy metals into groundwater, contaminating drinking water sources.
7. Why is the depletion of the ozone layer in the stratosphere a major concern?
The depletion of the stratospheric ozone layer is a major concern because this layer acts as a protective shield against the sun's harmful ultraviolet (UV-B) radiation. When pollutants like CFCs break down the ozone molecules, they create an 'ozone hole,' allowing more UV-B rays to reach the Earth. This increased exposure can lead to a higher incidence of skin cancer, cataracts, and a weakened immune system in humans, as well as damage to marine ecosystems and plant life.
8. Why is carbon dioxide considered a pollutant if it's essential for plant life?
While carbon dioxide (CO₂) is essential for photosynthesis, its classification as a pollutant relates to its role in global warming. The issue is not its existence but its excessive concentration due to human activities like burning fossil fuels. This excess CO₂ enhances the greenhouse effect by trapping more heat in the Earth's atmosphere than is natural. The resulting rise in global temperatures causes climate change, making the overabundance of CO₂ a pollutant from an environmental balance perspective.
