All schools and colleges in Delhi will remain shut till Sunday due to alarming levels of pollution, Deputy Chief Minister Manish Sisodia announced on Wednesday."Delhi's air quality is getting worse. In this situation, there can be no compromise on children's health," Sisodia, also the Education Minister, said in a tweet.The directive came as the air quality in Delhi and NCR dropped to the "severe" level with an average range of dangerous PM2.5 particles measured at 475 micrograms per cubic meter in the region.The "severe" level between 400 and 500 of PM2.5 "affects healthy people and seriously impacts those with existing diseases", according to Central Pollution Control Board.