MEVE 019: Unit 01 - Air Pollution

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 UNIT 1: AIR POLLUTION

1.1 Introduction

Air pollution is one of the most serious environmental challenges facing humanity today. It affects human health, contributes to climate change, and degrades the natural environment. With the growth of industrialization, urbanization, and vehicular movement, the concentration of pollutants in the atmosphere has significantly increased. This unit provides a comprehensive understanding of the sources, types, effects, and management of air pollutants.

1.2 Objectives

After completing this unit, you will be able to:

·         Define air pollution and identify its main sources.

·         Differentiate between primary and secondary air pollutants.

·         Understand the formation and effects of tropospheric ozone and smog.

·         Examine the impact of volatile organic compounds (VOCs).

·         Analyze the processes of atmospheric deposition and acid precipitation.

·         Learn about management strategies to control air pollution.

1.3 Definition of Air Pollution

Air pollution refers to the presence of substances in the air that are harmful to humans, animals, plants, or the environment. These substances may be solid particles, liquid droplets, or gases. Air pollution can be natural (e.g., volcanic eruptions, forest fires) or man-made (e.g., industrial emissions, vehicle exhaust).

According to the World Health Organization (WHO), air pollution is the contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere.

1.4 Types of Air Pollutants and Their Sources

Air pollutants are categorized as primary and secondary based on their origin.

1.4.1 Primary Air Pollutants

These are emitted directly from a source into the atmosphere.

Examples:

·         Carbon monoxide (CO): Incomplete combustion of fossil fuels.

·         Sulphur dioxide (SO₂): Burning of coal and oil in power plants and industries.

·         Nitrogen oxides (NOₓ): Vehicles, power plants, combustion.

·         Particulate Matter (PM₁₀ and PM₂.₅): Construction, industries, burning biomass.

·         Volatile Organic Compounds (VOCs): Paints, fuels, solvents.

1.4.2 Secondary Air Pollutants

These are not emitted directly but form in the atmosphere through chemical reactions among primary pollutants.

Examples:

·         Tropospheric ozone (O₃)

·         Peroxyacetyl nitrate (PAN)

·         Acid rain (H₂SO₄ and HNO₃)

·         Photochemical smog

1.5 Tropospheric Ozone

Tropospheric ozone is a secondary pollutant formed close to the Earth's surface. Unlike stratospheric ozone, which protects us from ultraviolet radiation, ground-level ozone is harmful to health and the environment.

1.5.1 Tropospheric Ozone Formation

It is formed through photochemical reactions involving:

·         Nitrogen oxides (NOₓ)

·         Volatile organic compounds (VOCs)

·         Sunlight

The chemical reaction:

NO₂ + sunlight → NO + O
O + O₂ → O₃ (ozone)

1.5.2 Tropospheric Ozone Concentration

Ozone levels are typically higher during warm, sunny days. Urban areas with high vehicular and industrial activity often experience elevated ozone concentrations.

1.5.3 Health Impacts

·         Irritation of eyes, nose, and throat.

·         Worsening of asthma and respiratory conditions.

·         Reduced lung function and lung tissue damage.

·         Increases risk of cardiovascular diseases.

1.6 Volatile Organic Compounds (VOCs)

VOCs are organic chemicals that evaporate easily at room temperature and contribute significantly to the formation of ozone and smog.

1.6.1 Sources

·         Paints, varnishes, and cleaning products.

·         Fuel combustion (e.g., petrol and diesel engines).

·         Industrial processes.

·         Biomass burning and landfills.

1.6.2 Impacts

·         Contribute to ground-level ozone formation.

·         Health effects include eye irritation, headaches, and damage to the liver, kidneys, and central nervous system.

·         Long-term exposure can lead to cancer (e.g., benzene, formaldehyde).

1.6.3 Management and Policy

·         Regulatory control on VOC content in products.

·         Promotion of water-based or low-VOC alternatives.

·         Monitoring and setting permissible limits.

·         Use of emission control technologies in industries.

1.7 Atmospheric Deposition of Air Pollutants

Atmospheric deposition refers to the settling of airborne pollutants onto the Earth’s surface through rain, snow, fog, or dry particles.

1.7.1 Photochemical Smog

·         Occurs in sunny urban areas due to chemical reactions between NOₓ and VOCs.

·         Contains ozone, PAN, and other oxidants.

·         Leads to eye irritation, respiratory issues, and plant damage.

·         Example: Los Angeles-type smog.

1.7.2 Industrial Smog

·         Formed from industrial emissions (SO₂, smoke) mixing with fog or moisture.

·         Common in cold, damp climates with high coal usage.

·         Example: London smog of 1952.

1.7.3 Acid Precipitation

·         Occurs when SO₂ and NOₓ react with water vapor to form sulfuric and nitric acid.

·         Falls as acid rain, snow, fog, or dust.

·         Causes:

o    Acidification of lakes and rivers.

o    Damage to crops, forests, and buildings.

o    Soil degradation.

1.8 Let Us Sum Up

In this unit, we have learned that:

·         Air pollution is a major threat to health and the environment.

·         Primary pollutants are emitted directly; secondary pollutants form through reactions in the atmosphere.

·         Tropospheric ozone and VOCs are critical components of smog and have harmful effects.

·         Atmospheric deposition, smog, and acid rain are serious consequences of air pollution.

·         Managing air pollution requires both technological interventions and strong environmental policies.

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