With the change in the wind direction and slight rise in temperature, Delhi on Thursday recorded a slight improvement in the air quality which however remained "very poor" generally but the situation in the NCR was a little better.

According to the Central Pollution Control Board (CPCB), Delhi's Air Quality Index (AQI) was at 311 on Thursday against 355 on Wednesday, both considered "very poor". 

Several places in NCR, which were earlier suffering with "severe" air quality on Thursday saw improvement with the CPCB recording AQI at 325 in Haryana's Gurugram (against 354 on Wednesday), 321 in UP's Noida (344 on Wednesday), 352 in Ghaziabad (402 on Wednesday) and 372 in Rajasthan's Bhiwadi (417 on Wednesday).

Haryana's Faridabad, where air quality was being placed at "severe" or "very poor" since the past week, saw a considerable improvement on Thursday, with the AQI at 82 or "satisfactory" against "very poor" (347) on Wednesday and "severe" (410) on Tuesday.

In Delhi, the major pollutant PM2.5, or particles with diameter less than 2.5mm, also saw a slight drop mostly because the wind stopped entering from Punjab where stubble burning continues unabated.

The average PM2.5 value at 16 different areas of Delhi was 280, still 4.5 times more than the permissible limit.

Shadipur area in central Delhi was however most polluted with AQI still "severe" at 436 at 5 p.m. The PM2.5 value there was around 500 till 7 a.m. while it ranged between 382 to 305 from 8 a.m. onwards till 6 p.m.

Safe limit for PM2.5 is 60 (microgrammes per cubic metre) as per national standards and 25 internationally.

The PM2.5 levels at eight out of ten monitoring stations of System of Air Quality and Weather Forecasting and Research (SAFAR) were placed under "very poor" category, while slight improvement was seen at Pusa and Dhirpur (north Delhi).

The PM2.5 value at Dhirpur, Pitampura, Delhi University (north Delhi), Pusa (central Delhi), Lodhi Road, Mathura Road, Aya Nagar (south Delhi) and Delhi Airport (T3) as well as Noida and Gurugram ranged between 260 and 322 on Thursday, against 392 and 326 on Wednesday and 362 and 302 on Tuesday.

The trend in air quality improvement could however be short-lived, warn weather analysts as the wind are likely to change again Sunday onwards.

According to the weather forecast, from Wednesday onwards, cold and dry north-westerly winds which were bringing toxins from neighbouring Punjab and Haryana, due to stubble burning there, to Delhi had changed into warm but moist south-easterly winds, thereby giving slight breather to the Delhi-NCR for next two to three days.

"The south-easterly winds have a speed of about 13-14 kmph which is helping with dispersal of fine particles in Delhi-NCR's air. This for next three days would provide some window to cleanup," Mahesh Palawat, Director, private weather forecasting agency Skymet, told .