What is the main source of carbon monoxide (CO) in urban areas?

Step 1: Analyze the question The question asks for the main source of carbon monoxide (CO) specifically in urban areas. The key words are "main" and "urban."

Step 2: Explain the concept Carbon monoxide forms during incomplete combustion of carbon-containing fuels, when there isn't enough oxygen for the carbon to burn fully to CO₂:

2C + O₂ → 2CO (incomplete combustion) C + O₂ → CO₂ (complete combustion)

Petrol and diesel engines often operate with limited oxygen in the cylinder, especially in slow, stop-and-go traffic, so they release a lot of CO.

Step 3: Evaluate each option

• A. Volcanic eruptions: These do release CO, but they are natural, occasional, and not found in cities. Eliminate.
• B. Vehicle emissions: Cars, motorcycles (okadas), tricycles (keke), buses, and generators burn fuel incompletely. In cities like Lagos, Abuja, and Port Harcourt, heavy traffic makes this the dominant source of CO. Correct.
• C. Forest fires: These produce CO, but they happen in forests and rural or bush areas, not mainly in urban areas. Eliminate.
• D. Industrial processes: These contribute some CO, but their share is smaller than that of road transport in urban settings. Eliminate.

Step 4: Answer The main source of CO in urban areas is vehicle emissions, so the answer is B.

Exam tip: Remember "CO = Incomplete Combustion." Whenever a question mentions cities or urban areas with CO, think of vehicle exhaust. Also remember that CO is dangerous because it binds to haemoglobin to form carboxyhaemoglobin, which reduces the blood's ability to carry oxygen. This is why you should never run a generator in a closed room.