Air Pollution: Overview & Classification
1. Air Pollution: Overview
Definition: Air pollution occurs when harmful substances, known as pollutants, enter the air and disrupt the natural balance of the atmosphere. These pollutants can be gases, tiny particles, or biological molecules.
Impact:
🏥 Health
Breathing polluted air can cause respiratory infections, heart disease, stroke, and lung cancer. It affects the health of babies before birth and is linked to lower IQ and cognitive impairment.
🌍 Environment
Leads to climate change, ozone layer depletion, and habitat destruction.
🏢 Structures
Damages buildings (e.g., acid rain corrosion).
2. Classification of Air Pollutants
1. Primary Pollutants:
Emitted directly from a source.
- Carbon monoxide (CO) from car exhausts
- Sulfur dioxide (SO₂) from industrial processes
2. Secondary Pollutants:
Formed when primary pollutants react in the atmosphere.
📝 Asked in Exam: Sulphate, Photochemical smog, and PeroxyAcetyl Nitrate (PAN) are examples of secondary air pollutants.
- Ground-level Ozone: Forms when Hydrocarbons & NOₓ react with sunlight.
- Acid Rain: Caused by SO₂ & NOₓ reacting with water.
3. Particulate Matter (PM)
One of the parameters used to characterize the air quality at a location is PM. Here, the suffix '2.5' refers to the size of suspended particles in certain units (microns).
📝 Asked in Exam: The suffix in PM₂.₅ refers to the size of suspended particles in microns.
Classification by Size:
Coarse Particles (> 10 microns)
📝 Asked in Exam: Coarse particles are larger particles, typically greater than 10 microns in size.
- Generally not inhaled deeply
- Less significant indicators of health impacts compared to smaller particles
RSPM / PM₁₀
📝 Asked in Exam: RSPM typically refers to particulate matter with an aerodynamic diameter of less than 10 microns (PM₁₀).
📝 Asked in Exam: PM₁₀ is preferred over Total Suspended Particles (TSP) for air quality monitoring studies.
Fine Particles (PM₂.₅)
📝 Asked in Exam: Fine particles are those SPM whose aerodynamic diameter is less than 2.5 microns.
Sources: Combustion processes, Industrial processes, Vehicle exhaust.
Ultrafine Particles (< 0.1 microns)
📝 Asked in Exam: Ultrafine particles are the smallest particles, typically less than 0.1 microns in size.
Modes of Formation:
Nucleation Mode: < 0.01 microns. Formed from gas-to-particle conversion. (Finest PM)
Aitken Mode: 0.01 to 0.1 microns.
Accumulation Mode: 0.1 to 2.5 microns. Remains airborne for a long time.
Health Impact of PM:
📝 Asked in Exam: The most relevant effect of particulate matter in air on human health is the aggravation of respiratory disease.
Pathway in Human Body:
📝 Asked in Exam: Inhalation → Lungs → Blood → Organs
Inhalation
→
Lungs
→
Blood
→
Organs
Note: Atmospheric haze is mainly caused by ultra-fine size particulate matters.
Soot and Black Carbon:
📝 Asked in Exam: Soot particles (black carbon) are toxic substances that contribute to global warming and penetrate deep into lungs.
Black Carbon Aerosols:
- Absorb sunlight – warming the atmosphere
- Reduce ice/snow reflectivity – accelerating melting
4. Major Primary Pollutants
1. Carbon Monoxide (CO)
Colorless, odorless, tasteless, and highly toxic.
Source: Incomplete combustion (cars, coal).
📝 Asked in Exam: CO has a strong affinity towards haemoglobin (greater than oxygen). It forms Carboxyhemoglobin, reducing oxygen transport.
📝 Asked in Exam: CO is a serious asphyxiant; short exposure can be fatal.
2. Sulfur Dioxide (SO₂)
Pungent gas smelling like burnt matches.
📝 Asked in Exam: Major sources: Burning fossil fuels in power plants and smelting metal ores.
📝 Asked in Exam: Taj Mahal is mainly threatened by the deleterious effects of Sulphur dioxide (Acid Rain precursor).
3. Nitrogen Oxides (NOₓ)
📝 Asked in Exam: Includes Nitric oxide (NO) and Nitrogen dioxide (NO₂).
📝 Asked in Exam: Nitric oxide (NO) has the least residence time in the atmosphere.
📝 Asked in Exam: Key ingredient in photochemical smog formation.
4. Hydrocarbons / BTEX
BTEX: Benzene (Leukemia), Toluene (Nervous system), Ethylbenzene, Xylene.
5. Major Secondary Pollutants
1. Photochemical Smog ("Summer Smog")
📝 Asked in Exam: Requires NO₂, VOCs, AND Sunlight.
📝 Asked in Exam: More prevalent in summer. Causes eye/throat irritation and reduced visibility.
2. Peroxyacyl Nitrates (PANs)
Formed by oxidation of VOCs + NO₂ + Sunlight.
- Lachrymators: Cause eye irritation even at low levels.
- Mutagenic properties (skin cancer link).
3. Ground-Level Ozone (O₃)
Reaction between NOₓ, VOCs, and sunlight.
- Irritates eyes, throat, lungs; worsens asthma.
- Damages crops/forests.
4. Acid Rain
SOₓ + NOₓ + Water Vapor → Sulfuric & Nitric Acid.
📝 Asked in Exam: Rain is acid rain when pH < 5.6.
6. Volatile Organic Compounds (VOCs)
Organic chemicals with high vapor pressure (evaporate easily).
📝 Asked in Exam: Short-lived, unstable. Some are carcinogenic. Naturally oxidize to CO and CO₂.
Sources:
Natural Sources
📝 Asked in Exam: Trees, Plants, Bogs, Termites.
📝 Asked in Exam: Trees emit Isoprene (contributes to ozone) and Terpenes.
Anthropogenic Sources
📝 Asked in Exam: Vehicles, Power Plants, Room Deodorizers.
📝 Asked in Exam: Formaldehyde, Benzene, Toluene (Human-made sources).
Household: Paints, glues, aerosols, dry-cleaned clothes.
Impacts:
- Smog: Anthropogenic VOCs play a key role in photochemical smog.
- Water: Common groundwater contaminant.
- Health: Cancer risk; Formaldehyde is a serious allergen.
7. Persistent Organic Pollutants (POPs)
Toxic organic compounds resistant to environmental degradation.
📝 Asked in Exam: Widespread (Tropics to Arctic). Accumulate in food webs. Examples: PCBs, Dioxins, Furans.
Characteristics:
🌍 Global Spread: Travel via "Grasshopper effect".
🐟 Bioaccumulation: Accumulate in fatty tissues.
🛡️ Uses: Flame retardants, non-stick products (PFOS).
Types & Sources:
- Dirty Dozen: DDT, Aldrin, Chlordane, PCBs.
- Incineration By-products: Dioxins and Furans (from burning plastics/waste). (Highly Toxic)
Health Effects:
- Acute: Allergies, Hypersensitivity, Death.
- Chronic: Nervous system damage, Endocrine disruption, Diabetes link.
- Developmental: Immune disruption.
8. Related Concepts
🤧 Allergens
Substances that activate the immune system.
💨 Carbon Monoxide
Asphyxiant.
🫁 Nitrogen Dioxide
Respiratory problems, "blue baby" syndrome.
😮💨 Ozone
Potent respiratory irritant and allergen.