Several days of hot weather mean London is facing an inevitable rise in air pollution as the Olympics get underway. The latest forecast shows pollution levels will be at moderate levels over the next 24 hours in London. The situation is expected to remain unchanged over the next few days.
The main concern is ground level ozone. It forms from traffic fumes in sunny weather, and can cause breathing difficulties.
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The Sherlock actor made the comment while he received an award for his humanitarian work.