On a day the United Nations Environment Programme (UNEP) marked world's first "Smog Day", to remember those who died due to air pollution, Delhi-NCR's air quality dipped to "severe" on Tuesday afternoon. While the observance of this day - December 5 - is inspired from the first day of the lethal smog that hit London in 1952 and which led to Britain's Clean Air Act, UNEP said that "estimated 18,000 people die every day worldwide as a result of air pollution".

Teenagers venture out on their bicycles amid heavy smog and air pollution in New Delhi. Pic/PTI