The permissible range for PM2.5 is 60 as per national standards and 25 by the international standards.
The worst PM2.5 situation was at Anand Vihar in east Delhi, highest at 410 and 492 between 10 am and 11:30 am.
Mandir Marg in central Delhi saw PM2.5 peaking up at 339 at 10 am, while in Punjabi Bagh in west Delhi, it was at 372 and the level ranged between 224 and 317 from 9 am to 11:30 am at RK Puram in south Delhi.
Air quality improved slightly from 1 pm onwards, but PM2.5 levels was still four to seven times over the safe limit, ranging between 123 and 184 at 17 locations across Delhi.
According to weather analysts, the sudden drop in air quality could be due to sudden change in wind directions, as the north-westerly winds from neighbouring Punjab and Haryana started entering Delhi again, changing from earlier short-spanned south-easterly winds.
"The speed of the winds is about 10 kmph. However, this time, north-westerly winds will be short spanned," Mahesh Palawat, director of private weather analyst Skymet said.
Sunday also saw a slight dip in minimum temperature.