Atmospheric and Environmental Chemistry

The One Thing

Atmospheric and environmental chemistry examines how the composition of air and the chemical changes involving pollutants affect organisms, materials, climate, and natural cycles. Pollution control therefore requires both scientific methods and responsible management of energy, transport, forests, and waste.

Reactions, Processes and Experiments

Key Terms

• Atmosphere: The envelope of gases surrounding Earth.
• Clean air: Air containing gases in their usual proportions and only very small amounts of impurities.
• Nitrogen: The most abundant gas in air, making up about 78% by volume; it is relatively unreactive and is essential for proteins and plant growth.
• Oxygen: A gas forming about 21% of air that supports respiration and combustion.
• Carbon dioxide: A gas present in a small amount, about 0.04% of air, used by green plants in photosynthesis and released during respiration and combustion.
• Noble gases: Very unreactive gases such as argon, neon, helium, and krypton; argon is present in the greatest amount, about 0.93% of air.
• Water vapour: Variable moisture in the atmosphere that forms clouds and participates in the water cycle.
• Air pollutant: Any solid, liquid, or gaseous substance present in air at a harmful concentration.
• Primary pollutant: A pollutant released directly from a source, such as carbon monoxide from incomplete combustion.
• Secondary pollutant: A harmful substance formed in the atmosphere by chemical reactions between primary pollutants and air components.
• Particulate matter: Tiny solid particles or liquid droplets suspended in air, including dust, smoke, soot, and fine particles.
• Carbon monoxide: A poisonous, colourless gas formed during incomplete combustion; it reduces the blood's ability to carry oxygen.
• Sulphur dioxide: A pungent gas mainly produced by burning sulphur-containing fuels; it can irritate the respiratory system and form acid rain.
• Nitrogen oxides: Gases such as nitrogen monoxide and nitrogen dioxide formed mainly in high-temperature engines and furnaces; they contribute to smog and acid rain.
• Ozone: A form of oxygen with formula O3; it protects life in the upper atmosphere but is harmful when present near the ground.
• Greenhouse effect: The warming of Earth's surface and lower atmosphere because gases such as carbon dioxide, methane, and water vapour absorb outgoing infrared radiation.
• Global warming: The long-term rise in Earth's average temperature, largely increased by human activities that add greenhouse gases.
• Acid rain: Rain or other precipitation made unusually acidic when sulphur dioxide and nitrogen oxides form acids in the atmosphere.
• Photochemical smog: A brownish haze formed when nitrogen oxides and hydrocarbons react in sunlight, producing ozone and other irritating substances.
• Ozone layer: A region of the stratosphere containing relatively high ozone concentration that absorbs much of the Sun's harmful ultraviolet radiation.
• CFCs: Chlorofluorocarbons formerly used in refrigeration and aerosols; they can release chlorine radicals that destroy stratospheric ozone.
• Biodegradable waste: Waste that microorganisms can decompose naturally, such as vegetable peels and paper.
• Non-biodegradable waste: Waste that does not decompose easily by natural processes, such as many plastics and some synthetic materials.
• Eutrophication: Excessive growth of algae in water due to nutrient enrichment, followed by oxygen depletion and harm to aquatic life.
• Sustainable development: Using resources to meet present needs without preventing future generations from meeting their needs.

Easily Confused

• Oxygen and combustion: Oxygen supports combustion but is not itself combustible.
• Nitrogen and oxygen: Nitrogen does not support combustion and dilutes oxygen in air, whereas oxygen supports combustion.
• Primary and secondary pollutants: A primary pollutant is released directly from a source, whereas a secondary pollutant forms in the atmosphere through chemical reactions.
• Stratospheric ozone and ground-level ozone: Stratospheric ozone absorbs harmful ultraviolet radiation, whereas ground-level ozone is a secondary pollutant that can damage lung tissue and plant leaves.
• Complete and incomplete combustion: Complete combustion of carbon forms carbon dioxide, whereas incomplete combustion can form poisonous carbon monoxide.
• Greenhouse effect and global warming: The greenhouse effect is a natural warming process necessary for life; global warming is the long-term rise in average temperature, largely increased by human activities.
• Biodegradable and non-biodegradable waste: Biodegradable waste can be decomposed naturally by microorganisms, whereas non-biodegradable waste does not decompose easily.
• Acid rain and photochemical smog: Acid rain results mainly from atmospheric acids formed from sulphur dioxide and nitrogen oxides; photochemical smog forms when nitrogen oxides and hydrocarbons react in sunlight.

What Gets Asked

• Air-composition questions: State the approximate composition of dry air: nitrogen 78%, oxygen 21%, argon and other noble gases about 0.93%, and carbon dioxide about 0.04%. Water vapour, dust, smoke, and other impurities are variable.
• Equation questions: Recall and balance the equations for photosynthesis, respiration, complete combustion of carbon, incomplete combustion of carbon, and acid formation. A common mark-losing error is confusing carbon dioxide, formed in complete combustion, with carbon monoxide, formed in incomplete combustion.
• Pollution-source and effect questions: Identify sources such as vehicle exhaust, factories, thermal power stations, burning coal and waste, construction dust, forest fires, and volcanic eruptions, and link pollutants to effects such as respiratory problems, reduced visibility, acid rain, smog, or climate change.
• Acid-rain questions: Explain that sulphur dioxide and nitrogen oxides form acids in the atmosphere. Marks are lost when damage to crops, forests, aquatic organisms, monuments, and limestone or marble buildings is omitted.
• Ozone questions: Distinguish the protective ozone layer from harmful ground-level ozone, and recall that CFCs can release chlorine radicals that destroy stratospheric ozone. The 1987 Montreal Protocol was designed to reduce substances that damage the ozone layer.
• Control and policy questions: Describe cleaner fuels, public transport, catalytic converters, electrostatic precipitators, scrubbers, filters, proper waste disposal, tree planting, and the principles reduce, reuse, and recycle. The 2015 Paris Agreement aims to strengthen global action against climate change and limit the rise in global average temperature.