Chemistry and the Environment

Introduction

The same chemistry that gives us fuels, fertilisers and plastics can harm air, water and soil when substances end up in the wrong place or in the wrong amounts. Understanding environmental chemistry helps us see how these problems arise and, just as importantly, how chemistry provides the tools to detect and solve them. This page introduces key environmental issues and the responsible actions that individuals, industries and governments can take.

Core explanation

Air pollution. Burning fuels in vehicles, power stations and factories releases pollutants. Sulfur dioxide comes from sulfur impurities in coal and some oils; nitrogen oxides form when nitrogen and oxygen from the air react at the high temperatures inside engines. These gases dissolve in rain to form acids, producing acid rain that damages buildings, forests and lakes. Incomplete combustion produces carbon monoxide, a poisonous gas, and tiny soot particles that harm the lungs.

Climate change. Carbon dioxide and methane are greenhouse gases : they let sunlight through but absorb some of the heat radiated back by the Earth, keeping the planet warmer. Their concentrations have risen significantly since industrialisation, mainly from burning fossil fuels and from agriculture, and this is changing the global climate.

Water pollution. Excess fertilisers and untreated sewage add nutrients to rivers and lakes, causing rapid growth of algae. When the algae die, bacteria that decompose them use up oxygen in the water, and fish may die. Heavy metals such as lead and mercury, and some industrial chemicals, can be toxic even in small amounts.

Land and plastic pollution. Many plastics are not biodegradable and can remain in the environment for a very long time, breaking into tiny pieces called microplastics.

Ozone depletion. Some chemicals once used in refrigerators and aerosol sprays, called CFCs, drifted into the upper atmosphere and destroyed ozone, which protects life from ultraviolet radiation. An international agreement, the Montreal Protocol, phased them out, and the ozone layer is gradually recovering — a success story for science-based action.

Chemistry as part of the solution. Chemists measure pollutants accurately, trace their sources and develop solutions: catalytic converters that turn car exhaust pollutants into less harmful gases, scrubbers that remove sulfur dioxide from power-station chimneys, water-treatment processes, biodegradable materials, cleaner fuels and batteries for renewable energy. The approach known as green chemistry aims to design processes that avoid producing hazardous substances in the first place.

Step-by-step reasoning

To analyse an environmental problem:

1. Identify the substance causing harm. 2. Identify its source (for example, burning coal or fertiliser runoff). 3. Describe the chemical or biological process that causes the harm. 4. Suggest solutions at the source (prevention) and after release (treatment).

Visual explanation

Problem Main chemical cause Effect Chemical solution --- --- --- --- Acid rain SO₂ and nitrogen oxides Damages lakes, forests, buildings Remove sulfur from fuels; scrubbers Climate change CO₂, methane Rising global temperatures Renewable energy, efficiency Algal blooms Excess nitrates and phosphates Low oxygen, fish deaths Careful fertiliser use, sewage treatment Ozone loss CFCs More UV reaching the ground Montreal Protocol; CFC substitutes

Real-world analogy

Pollution is like leaving a tap running in a bathtub with a blocked drain. At first nothing seems wrong, but the water level keeps rising until it overflows. Many pollutants build up slowly in air, water or soil until they reach harmful levels. Turning off the tap (reducing emissions) is usually better than mopping up the floor later.

Real-world example

Catalytic converters in cars contain metals such as platinum, palladium and rhodium. As hot exhaust passes over them, harmful carbon monoxide, unburnt hydrocarbons and nitrogen oxides are converted into carbon dioxide, water and nitrogen. The catalyst speeds up these reactions without being used up, greatly reducing urban air pollution.

Why?

Why did the Montreal Protocol work so well? Scientists produced clear evidence linking CFCs to ozone destruction, measured the damage, and chemists developed substitute substances for refrigerators and sprays. Governments then agreed to phase CFCs out. Good science, practical alternatives and international cooperation together solved a global chemical problem.

Common misconception

Some people confuse the ozone hole with global warming. They are different problems with different causes: the ozone hole was caused mainly by CFCs destroying ozone, while global warming is caused mainly by increased greenhouse gases such as carbon dioxide. Some substances, however, affect both.

Worked example

Question: Explain how burning coal containing sulfur can damage a lake many kilometres away.

Reasoning: Follow the substance from source to effect.

Answer: Sulfur in the coal burns to form sulfur dioxide. The gas is carried by wind, dissolves in rainwater and forms acids. This acid rain falls into the distant lake, lowering its pH and harming fish and other aquatic life.

Quick check

1. Name two greenhouse gases. Answer: Carbon dioxide and methane (water vapour and nitrous oxide are also acceptable).

Exam focus

Environmental questions usually ask for source, effect and solution. Link each pollutant to its specific source and effect; do not mix up acid rain, global warming and ozone depletion. Naming a specific solution, such as catalytic converters, earns more credit than general advice.

Advanced insight

Ozone destruction by CFCs involves chain reactions: ultraviolet light releases chlorine atoms, and each chlorine atom can destroy many ozone molecules before it is removed. You will study chain reactions in the Reaction Lab and later in atmospheric chemistry, where the same type of mechanism explains several environmental processes.

Summary

Chemical pollution includes acid rain from sulfur and nitrogen oxides, climate change from greenhouse gases, water pollution from excess nutrients and toxic metals, persistent plastics and ozone depletion from CFCs. Chemistry also provides solutions: accurate measurement, catalytic converters, scrubbers, water treatment, green chemistry and international agreements based on evidence.

Practice questions

1. What causes acid rain? Answer: Sulfur dioxide and nitrogen oxides from burning fuels dissolve in rainwater to form acids. 2. Explain why excess fertiliser in a lake can kill fish. Answer: Nutrients cause rapid algae growth; when the algae die, bacteria decomposing them use up the oxygen in the water, so fish suffocate. 3. What does a catalytic converter do? Answer: It speeds up reactions that convert harmful exhaust gases (CO, unburnt hydrocarbons, nitrogen oxides) into less harmful gases (CO₂, H₂O, N₂). 4. Why is the Montreal Protocol considered a success? Answer: It phased out ozone-destroying CFCs worldwide, and the ozone layer is gradually recovering.