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What is it?
Nitrogen dioxide (NO₂) is a gas produced mainly by burning fossil fuels - especially diesel and petrol engines in road traffic. Readings are measured in micrograms per cubic metre of air (µg/m³).
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Why is it harmful?
NO₂ irritates the airways and lungs. Regular exposure is linked to asthma, reduced lung development in children, and increased risk of respiratory and cardiovascular disease.
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What are the limits?
The WHO recommends an annual mean of no more than 10 µg/m³ to protect health. The UK legal limit is 40 µg/m³ - four times higher. All readings on this chart are above the WHO guideline.