Industrial Gaseous Waste and Air Pollution
Industrial Gaseous Waste and Air Pollution
Nitrogen (N₂), oxygen (O₂), and carbon dioxide (CO₂) remain in the atmosphere in a specific ratio, maintaining the ecological balance. Variations in the quantity of these components due to natural or anthropogenic causes lead to environmental disasters and air pollution.
Main Sources of Air Pollution:
- Sulfur dioxide (SO₂) and Sulfur trioxide (SO₃)
- Carbon monoxide (CO) and Carbon dioxide (CO₂)
- Nitrogen oxides (NOₓ: NO, NO₂)
- Hydrogen sulfide (H₂S) and Ammonia (NH₃)
- Volatile Hydrocarbons (e.g., CH₄, C₆H₆)
- Various metallic particles or metallic oxides (e.g., ZnO, Lead particles)
- Dust, ash (fly ash), and smoke
2. Air Pollutants:
Any substance present in the environment in a concentration higher than its natural abundance, causing adverse effects on human life or other organisms, is called a pollutant. For example, CO₂ exists naturally in the air, but if its concentration increases to 0.03% or more, it is considered a pollutant.
Classification of Pollutants:
- Primary Pollutants: Pollutants emitted directly from a source into the environment in an unchanged state. Examples: CO, CO₂, SO₂, NO, NO₂, hydrocarbons, ash, dust.
- Secondary Pollutants: Pollutants not emitted directly but formed through chemical reactions between primary pollutants or with other atmospheric components. Examples: Peroxyacetyl nitrate (PAN), ozone (O₃), sulfur trioxide (SO₃), sulfuric acid (H₂SO₄), dimethyl mercury (CH₃)₂Hg.
Key Terminology:
- Receptor: The specific part of the ecosystem, flora, or architectural structure severely affected by pollutants (e.g., acid rain affects living organisms, plants, or limestone architecture).
- Sink: Any environmental medium that continuously absorbs and reduces pollutants from the environment. Example: Ocean water and plants are the primary sinks for atmospheric CO₂.
- Threshold Limiting Value (TLV): The specific concentration of an existing pollutant beyond which the environment and living organisms are harmed.
Table: WHO Guidelines for Safe Threshold Limiting Values (TLV) of Air Pollutants:
| Gas | Safe Threshold Limiting Value (TLV) |
|---|---|
| Sulfur dioxide (SO₂) | 0.03 ppm |
| Sulfur trioxide (SO₃) | 0.05 ppm |
| Carbon dioxide (CO₂) | 350 ppm |
| Carbon monoxide (CO) | 9 ppm |
| Nitrogen dioxide (NO₂) | 0.05 ppm |
| Nitric oxide (NO) | 0.05 ppm |
| Methane (CH₄) | 1.5 ppm |
| Hydrogen sulfide (H₂S) | 0.05 ppm |
3. Detailed Description of Major Air Pollutants:
1. Carbon Monoxide (CO)
Sources: Incomplete combustion of fossil fuels, vehicle emissions, agricultural waste burning, metallurgical industries, petroleum extraction, volcanic eruptions, and forest fires.
Effects: A colorless, odorless, and tasteless toxic gas known as the “Silent Killer.” It enters the bloodstream and binds with hemoglobin 200 times faster than oxygen, forming a stable compound that blocks oxygen transport. High levels cause heart disease and death. It also inhibits nitrogen fixation in plants.
CO poisoning (oxygen replacement): HbO₂ + CO → HbCO + O₂
Reaction with iron in blood: Fe + 5CO → Fe(CO)₅
2. Sulfur Dioxide (SO₂)
Sources: Fossil fuel combustion, metallurgical industries, oil refineries, sulfuric acid production, and steel manufacturing. Volcanic eruptions release gases containing 40-70% SO₂.
Effects: An acidic gas that causes eye and respiratory tract irritation, asthma, bronchitis, and allergies. It causes ‘Chlorosis’ (loss of chlorophyll) in plants, hindering growth. Its major environmental impact is acid rain.
3. Nitrogen Oxides (NOₓ: NO, NO₂)
Sources: Fertilizer production/use, Nitric acid (HNO₃) production, steel factories, nuclear explosions, and high-temperature lightning in the atmosphere.
Effects: NO₂ is a toxic, acidic brownish gas. High exposure causes lung inflammation, bronchitis, and pneumonia. NO₂ causes photochemical smog, leading to eye irritation and breathing difficulties. Its major impact is acid rain.
4. Hydrogen Sulfide (H₂S)
Sources: Volcanic gas, decomposition of sulfur-rich organic matter (e.g., fish, eggs, high-protein waste), petroleum refining, paper industry, and sulfuric acid factories.
Effects: Highly toxic acidic gas with a rotten-egg smell. Its toxicity is nearly equal to Hydrogen Cyanide (HCN). Causes headaches, nausea, eye and throat irritation, and loss of appetite. High levels can be fatal as it reacts with vital body proteins.
5. Hydrocarbons (Mainly Methane, CH₄)
Sources: Paddy fields, swamps, livestock waste decomposition, incomplete fuel combustion, coal distillation, and industrial solvents (e.g., benzene, toluene).
Effects: Methane acts as a potent greenhouse gas, increasing global warming. High levels of polycyclic aromatic hydrocarbons (e.g., Benzopyrene, C₂₀H₁₂) can cause lung cancer. In the presence of sunlight, they form photochemical smog.
4. Photochemical Smog Formation:
Automobile engines release NO₂ gas, which reacts with atmospheric oxygen to form Ozone (O₃). In sunlight, this O₃ breaks down into reactive ozone (O) and free radicals, which combine with hydrocarbons to form Peroxyacetyl Nitrate (PAN). This creates a brownish haze known as photochemical smog.
O + O₂ → O₃
O₃ + Hydrocarbon → PAN (Peroxyacetyl Nitrate)
5. Particulates and Occupational Diseases:
Small solid or liquid particles with diameters between 10⁻³ and 10⁻⁶ m are called particulates. The extremely small ones are called aerosols.
- Stomatal Blockage: Particles settle on leaves, blocking stomata, inhibiting photosynthesis, and reducing crop yields.
- Lead (Pb) Impact: Lead from vehicle exhaust causes brain damage in children, nervous disorders, and hinders Red Blood Cell (RBC) development.
Occupational Lung Diseases:
| Industry/Worker | Disease | Responsible Particle/Cause |
|---|---|---|
| Coal Miner | Black Lung Disease | Coal dust |
| Textile Worker | White Lung Disease | Cotton fibers |
| Asbestos Factory Worker | Asbestosis | Asbestos particles |
| Cement & Stone Crushing | Silicosis | Silica or Quartz particles (SiO₂) |
A. Knowledge-Based Questions & Answers (Marks: 1)
1. What is an Air Pollutant?
Answer: Any substance present in the environment in a concentration higher than its natural abundance, causing adverse effects on humans or other organisms, is called an air pollutant.
2. What is a Primary Air Pollutant?
Answer: Pollutants that are emitted directly into the environment from a source in an unchanged state and cause air pollution are called primary air pollutants.
3. What is a Secondary Air Pollutant?
Answer: Pollutants that are not emitted directly from a source but are formed through chemical reactions between primary pollutants or with other atmospheric components are called secondary air pollutants.
4. What is a Receptor in terms of pollution?
Answer: The specific part of the ecosystem, flora, or architectural structure that is severely damaged by the influence of a pollutant is called a receptor.
5. What is a Sink?
Answer: If any environmental medium continuously absorbs a pollutant through chemical reaction and reduces its quantity in the environment, that medium is called a sink.
6. What are the main sinks for CO₂ in the atmosphere?
Answer: The main sinks for atmospheric CO₂ are ocean water and vegetation (plants).
7. What is the full form of TLV?
Answer: The full form of TLV is Threshold Limiting Value.
8. What is TLV?
Answer: The specific concentration of a pollutant in the environment beyond which the environment and living organisms are harmed is called TLV.
9. What is the safe TLV for SO₂ as per WHO?
Answer: As per WHO guidelines, the safe TLV for SO₂ is 0.03 ppm.
10. What is the safe TLV for SO₃ as per WHO?
Answer: As per WHO guidelines, the safe TLV for SO₃ is 0.05 ppm.
11. Which gas is called the “Silent Killer”?
Answer: Carbon monoxide (CO) gas is known as the “Silent Killer.”
12. What is Carboxyhemoglobin (HbCO)?
Answer: The stable complex compound formed by the reaction of Carbon monoxide (CO) with blood hemoglobin (Hb) is called carboxyhemoglobin.
13. What is Chlorosis?
Answer: The process of destruction of green chlorophyll in plants due to the effect of sulfur dioxide (SO₂) gas, which hampers plant growth, is called chlorosis.
14. What is Photochemical Smog?
Answer: The brownish haze created by a mixture of Peroxyacetyl nitrate (PAN), ozone (O₃), etc., formed by the reaction of nitrogen oxides (NOₓ) and volatile hydrocarbons in the presence of sunlight, is called photochemical smog.
15. What is the full form of PAN?
Answer: The full form of PAN is Peroxyacetyl Nitrate.
16. What is an Aerosol?
Answer: Among the particulates suspended in the air, those with extremely small diameters are called aerosols.
17. What are Particulates?
Answer: Tiny solid and liquid particles floating in the air (e.g., dust, ash, metal oxides) are called particulates.
18. What is Silicosis?
Answer: A complex lung disease caused by the continuous inhalation of silica or quartz (SiO₂) dust particles is called silicosis.
19. Which disease do coal miners suffer from?
Answer: Coal miners suffer from Black Lung disease.
20. What is the occupational lung disease of textile workers?
Answer: Textile workers suffer from White Lung disease.
21. Which material is responsible for Asbestosis?
Answer: Fine asbestos particles from asbestos factories are responsible for Asbestosis.
22. What percentage of SO₂ is released in volcanic eruptions?
Answer: Volcanic eruptions release gases containing approximately 40-70% SO₂.
B. Comprehension Questions & Answers (Marks: 2)
4NO₂ + O₂ + 2H₂O → 4HNO₃
C. Multiple Choice Questions (MCQ) & Answers
