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Illegal crop burning in the farm states surrounding New Delhi, vehicle exhaust emissions in a city with limited public transport and swirling construction dust have caused the crisis, which arises every year. The problem has been compounded this year by still conditions, the weather office said. A US embassy measure of tiny particulate matter PM 2.5 showed a reading of 608 at 10am when the safe limit is 50. An hour before it was 591.

GETTY Delhi has declared a pollution emergency and banned the entry of trucks and construction activity

GETTY The pollution has been compounded this year by still conditions claim the weather office

REUTERS Prince Charles and Camilla at the India Gate war memorial

I'd like to assure people that the central government shall do everything possible to bring about improvement in air quality in Delhi Harsh Vardhan - Federal environment minister

PM 2.5 is particulate matter about 30 times finer than a human hair. The particles can be inhaled deep into the lungs, causing heart attacks, strokes, lung cancer and respiratory diseases. Residents complained of headaches, coughs and smarting eyes. Many stayed home and restaurants in some of the city's most crowded parts were deserted. “I'd like to assure people that the central government shall do everything possible to bring about improvement in air quality in Delhi and the Nation Capital Region,” federal environment minister Harsh Vardhan said as authorities faced criticism for failing to take steps to fight a problem that erupts every year. The haze covered India Gate, a war memorial in the centre of the city where the Prince of Wales and the Duchess of Cornwall were due to pay respects in a two-day trip ending today.

Prince Charles & Camilla in pictures Mon, December 18, 2017 The Prince of Wales, Prince Charles, and Duchess of Cornwall royal visits and encounters across the globe. Play slideshow PA 1 of 100 The picture used on the Prince of Wales and Duchess of Cornwall's 2017 Christmas card which was taken by Hugo Burnand showing the royal couple in the Orchard Room during the private 70th birthday party of The Duchess of Cornwall at Highgrove

Schools have been shut for the week and late yesterday the city administration announced a set of measures to try to clean up the air. Commercial trucks have been banned from the city unless they are transporting essential commodities, all construction has been stopped and car parking charges raised four times to force residents to use public transport. The Delhi transport department said it would take a decision later in the day on whether to introduce an “odd-even” scheme under which cars with licence plates ending in an odd number are allowed one day and even-numbered cars the next. But experts said these measures were unlikely to bring immediate relief.

GETTY US embassy measure of PM 2.5 showed a reading of 608 at 10am when the safe limit is 50