Human Impact on the Environment
Ecology and the Environment · 8 question types
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 10% of your exam marks.
Climate change, deforestation, and biodiversity loss are growing in frequency as contemporary issues.
Industrial activity, road traffic, power stations and agriculture release several pollutants into the air. The two most important are and .
Carbon monoxide (CO)
Where it comes from: incomplete combustion of fossil fuels. Petrol engines, faulty gas boilers, badly-ventilated coal fires, and forest fires all produce carbon monoxide.
How it harms people: carbon monoxide binds to haemoglobin in red blood cells in the same place that oxygen would normally bind. It binds much more strongly than oxygen does, so while it is attached the haemoglobin can no longer carry oxygen. Even small concentrations of CO in the blood reduce its oxygen-carrying capacity, causing:
- Headache, dizziness and confusion at low doses
- Suffocation and death at higher doses
Carbon monoxide is odourless and invisible, which is why home CO detectors are required by law in many countries.
Sulfur dioxide (SO₂)
Where it comes from: burning of coal and oil that contain sulfur impurities. Coal-fired power stations, diesel engines and some volcanic eruptions all release SO₂.
How it causes acid rain: sulfur dioxide gas reacts with water vapour in the atmosphere to form sulfuric acid (and a similar process happens with nitrogen oxides forming nitric acid). These acids dissolve in rain, snow or fog, lowering the rain's pH to as low as pH 3 (compared to normal rainwater at about pH 5.6).
How it harms people: irritates the airways and lungs. Can trigger or worsen asthma. Long-term exposure raises the risk of bronchitis and other respiratory diseases.