Greenhouse gases, climate change and atmospheric pollutants

Chemistry · Chemistry of the atmosphere. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Greenhouse gases keep the Earth warm enough for life. Short wavelength radiation from the Sun passes through the atmosphere and warms the surface. The surface gives out longer wavelength infrared radiation, and greenhouse gases absorb it and send it out again in all directions, so less energy escapes to space.

Human activities add more of these gases. Most scientists agree, from peer-reviewed evidence, that this is raising the average temperature and causing climate change. The climate is very complex, so models are simplified and predictions are uncertain.

Burning fuels also releases pollutants: carbon monoxide, soot, sulfur dioxide and oxides of nitrogen. Each has its own cause and its own effect.

Rules to remember

The main greenhouse gases are carbon dioxide, methane and water vapour.
More carbon dioxide: burning fossil fuels and cutting down forests. More methane: cattle, rice fields and landfill sites.
Effects of climate change: rising sea levels and flooding, more extreme weather, changes in rainfall, and changes to where crops and wildlife can live.
Carbon footprint: the total amount of carbon dioxide and other greenhouse gases given out over the full life cycle of a product, service or event.
Incomplete combustion (too little oxygen) gives carbon monoxide, a toxic gas with no colour or smell, and soot (carbon particles), which causes global dimming and breathing problems.
Sulfur dioxide comes from sulfur impurities in the fuel; oxides of nitrogen form when nitrogen and oxygen from the air react in a hot engine. Both cause acid rain and breathing problems.

Common mistake

Students say greenhouse gases trap the light coming from the Sun, or mix the greenhouse effect up with the ozone layer. Greenhouse gases absorb the infrared radiation given out by the Earth's surface.

Worked example

A fuel that contains sulfur impurities is burned in a very hot engine with plenty of air. Which two pollutants are most likely to form: carbon monoxide, soot, sulfur dioxide, oxides of nitrogen?

Plenty of air means combustion is complete, so carbon monoxide and soot are not expected.
The sulfur in the fuel burns to give sulfur dioxide.
At the high temperature of the engine, nitrogen and oxygen from the air react to give oxides of nitrogen.

Answer: Sulfur dioxide and oxides of nitrogen, which both cause acid rain and breathing problems.

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