Coincidentally, as of Wednesday afternoon, all 6 air quality reporting stations run by the Delhi Pollution Control Committee have stopped reporting live data.
The US EPA states that when PM2.5 levels go above 300 micrograms/cubic meter everyone should take measures to protect themselves from exposure.
http://beijing.usembassy-china.org.cn/20130201-pm25-steps.html
Recent conditions in Delhi have surpassed pollution problems faced in Shanghai and other Chinese cities. Sources have claimed that the number of patients seeking treatment for respiratory and cardiac diseases in Delhi has risen by about a quarter since the pollution levels began to skyrocket on Monday.
http://in.reuters.com/article/2013/12/18/india-delhi-winter-smog-idINDEE9BH0D420131218
See my previous post on HN with more references.
https://news.ycombinator.com/item?id=6926518