Environmental Management (0680) | Atmospheric pollution and its causes

Welcome to Section 7: The Atmosphere and Human Activities!

Hi there! This chapter focuses on how our actions pollute the air we breathe and what happens as a result. Don't worry if some of the concepts sound technical; we'll break them down using simple language and everyday examples.
Understanding atmospheric pollution is essential because it affects everything from the quality of the air in our cities to the stability of the global climate. Let's get started!

7.2 Atmospheric Pollution and its Causes (The Four Big Issues)

The syllabus focuses on four main types of atmospheric pollution caused by human activity. We need to know exactly what causes each one.

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1. Smog (Smoke + Fog)

Smog is basically a thick, murky layer of polluted air near the ground. It makes breathing difficult and visibility poor.

The Two Main Causes of Smog

1. Vehicle Emissions: Cars, trucks, and buses release several harmful gases and tiny particles (particulates). The most relevant for smog are Oxides of Nitrogen (NOx) and unburnt hydrocarbons (or Volatile Organic Compounds, VOCs).
2. Volatile Organic Compounds (VOCs) from Industrial Processes: These are chemicals that easily turn into gas at room temperature (like paint fumes or solvent smells). Factories, petrol stations, and chemical plants release these.

How Photochemical Smog Forms (The Sunny Recipe)

Smog often forms in hot, sunny urban areas. This is called photochemical smog because it needs sunlight (photo-) to react with the pollutants.

• Step 1: NOx and VOCs are released throughout the day.
• Step 2: Strong sunlight provides the energy needed for these chemicals to react with each other and with oxygen in the air.
• Step 3: This reaction creates powerful secondary pollutants, most notably ozone (O₃, when found near the ground, it's harmful!) and other toxic compounds.

The Impact of Temperature Inversion

This is a key concept! Normally, warm air near the surface rises and takes pollutants high up where they disperse.

A Temperature Inversion happens when a layer of *warm* air settles above a layer of *cooler* air near the ground.
Analogy: Imagine putting a lid on a saucepan. The warm layer acts like a lid, trapping the cold air and all the pollutants beneath it.

• This trapping prevents the smog from rising and dispersing, making the pollution levels dangerously high until the sun or wind breaks the inversion layer.

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2. Acid Rain

Acid rain is any form of precipitation (rain, snow, fog) that is more acidic than normal. It's an issue that often travels across borders, affecting areas far from where the pollution was created.

The Culprits: What makes the rain acidic?

Acid rain is caused by two main groups of pollutants:

1. Sulfur Dioxide (SO₂): The biggest cause of acid rain.
   • Primary Source: Burning fossil fuels, especially coal, in power stations and industrial boilers. Coal often contains sulfur, which is released as SO₂ when burned.
2. Oxides of Nitrogen (NOx): (Nitrogen Monoxide and Nitrogen Dioxide).
   • Primary Source: High-temperature combustion in vehicle engines and thermal power stations.

The Process: From Gas to Acid

When SO₂ and NOx are released into the atmosphere, they react with water vapour, oxygen, and other chemicals to form weak acids:

• SO₂ turns into Sulfuric Acid (\(\text{H}_2\text{SO}_4\)).
• NOx turns into Nitric Acid (\(\text{HNO}_3\)).

Analogy: Think of these pollutants as dissolving like sugar in tea, but instead of making it sweet, they make the rainwater corrosive (acidic). This acidic water then falls as rain.

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3. Ozone Layer Depletion

This is different from smog! Smog involves harmful ozone at ground level (the troposphere). Ozone layer depletion concerns the loss of useful ozone high up in the atmosphere (the stratosphere).

What is the Ozone Layer?

The ozone layer is a shield in the stratosphere that absorbs most of the Sun's harmful Ultraviolet (UV) radiation. Without it, life on Earth would be severely damaged.

The Cause: Chlorofluorocarbons (CFCs)

The main substances responsible for destroying this protective layer are Chlorofluorocarbons (CFCs).

• Source: CFCs were historically used in:
  • Aerosol spray cans (as propellants)
  • Refrigerators and air conditioners (as coolants)
  • Foam packaging and solvents

How CFCs Cause Depletion (Step-by-Step)

CFCs are incredibly stable, meaning they can last for many decades.

1. CFCs are released and slowly drift up to the stratosphere.
2. Once there, high-energy UV radiation breaks down the CFC molecules.
3. This process releases a single chlorine atom (Cl).
4. This single chlorine atom acts as a catalyst, destroying thousands of ozone molecules (O₃) before it is finally removed from the atmosphere.

Did you know? One chlorine atom can destroy over 100,000 ozone molecules! This makes CFCs incredibly potent pollutants, even in tiny amounts.

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4. Enhanced Greenhouse Effect (Climate Change)

First, remember the Natural Greenhouse Effect (covered in 7.1) is vital—it keeps the Earth warm enough to support life. The problem is the enhanced (or human-caused) effect, which traps too much heat and causes global warming.

The Cause: Increased Greenhouse Gases (GHGs)

Human activities are increasing the concentration of gases that trap heat in the atmosphere. The syllabus highlights three main gases:

1. Carbon Dioxide (CO₂)
   • Primary Source: Burning fossil fuels (coal, oil, gas) for electricity, transport, and industry. Also, deforestation (trees absorb CO₂).
2. Methane (\(\text{CH}_4\))
   • Primary Source: Livestock farming (cows release methane), decay of waste in landfill sites, and rice cultivation in flooded fields.
3. Water Vapour (\(\text{H}_2\text{O}\))
   • Note: Water vapour is the most abundant natural greenhouse gas. While its increase is mainly a *response* to warming (a positive feedback loop), it is listed as a greenhouse gas contributing to the effect.

The Process: Trapping Extra Heat

The Earth absorbs solar radiation and re-radiates it as heat (infrared radiation). Greenhouse gases naturally absorb some of this heat, sending it back to Earth.

Analogy: Adding more GHGs is like adding an extra blanket to the Earth. The more blankets we add, the more heat is trapped, leading to an overall increase in global temperature (global warming).

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Chapter Summary: Know Your Pollutants!

When studying causes, remember these four key pollutants and where they come from:

• Smog: NOx and VOCs (mainly vehicles/industry).
• Acid Rain: SO₂ (coal/industry) and NOx (vehicles/power).
• Ozone Depletion: CFCs (old aerosols/refrigerants).
• Enhanced Global Warming: CO₂ and Methane (fossil fuels/agriculture/landfills).

Don't worry if this chapter felt heavy! The key is to link the pollutant name directly to the specific human activity (e.g., SO₂ to coal power). Keep practicing those links, and you'll ace this section!