Photochemical smog, the brown haze over busy cities on sunny days, forms when

sulphur dioxide from coal mixes with fog on cold nightsCorrect answerYour answersea salt is blown over the cityCorrect answerYour answerthe ozone layer comes down to the groundCorrect answerYour answernitrogen oxides and hydrocarbons from vehicles react in sunlight, making ground-level ozoneCorrect answerYour answer

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CorrectNot quiteAnswer D

Correct answer: D

Vehicle exhaust supplies nitrogen oxides and unburnt hydrocarbons.
Sunlight drives reactions between them that produce ozone and other irritants such as PAN, which sting the eyes and harm the lungs.

Worth noting

Smoke mixed with fog from burning coal is the older, sulphurous 'London' smog, which forms in cold, damp weather.

Concept: Photochemical smog
Typical timeTypical: 90 s
Your timeYours: —

The rule this testsAir, water, soil and noise pollution

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Ten questions from Pollution, Climate and Conventions, at your own pace.

Photochemical smog, the brown haze over busy cities on sunny days, forms when

Explanation