A smoky haze continued to envelop Delhi and nearby cities for the third straight day on Thursday, even as the air quality index showed signs of slight improvement. The Centre-run System of Air Quality and Weather Forecasting and Research, or SAFAR, recorded an overall index of 392 at 10.45 am, which lies in the “very poor” category.

However, the Central Pollution Control Board still displayed a “severe” reading of 411 at 10 am, as it calculates a 24-hour average. As the day progresses, this index reading may also come down. The air quality index has been in the “severe” zone for much of this week so far. At 4 pm on Wednesday, the CPCB’s index was at 419.

The 24-hour average was the worst for Anand Vihar locality, which was at 467 at 10 am. Vasundhara locality in Ghaziabad had an index of 462, Gurugram was at 340, and Noida Sector 62 at 459.

Meanwhile, Union Home Minister Amit Shah flagged off the “Run for Unity” in New Delhi to mark the birth anniversary of Sardar Vallabhbhai Patel amid the polluted environment. The run began at the Major Dhyan Chand National Stadium, even as doctors advised residents to take precautions such as wearing face masks and avoiding early morning and late evening walks due to the pollution, PTI reported.

The Delhi government has identified five “critically polluted” areas – Wazirpur, Anand Vihar, Ashok Vihar, Vivek Vihar and Bawana. Deputy Chief Minister Manish Sisodia said schools may be shut “when the need arises”.

Air in the severe category “affects healthy people and seriously impacts those with existing diseases”. SAFAR had predicted a marginal improvement in the air quality on Thursday due to an expected increase in wind speed that will help disperse pollutants faster.

The haze can be “purely” attributed to stubble burning in nearby states, whose share in Delhi’s pollution rose to the season’s highest of 35% on Wednesday, said SAFAR.