Delhi's air quality plunged to "very poor" category on Friday, owing primarily to unfavourable wind speed.
The PM2.5 -- particles in the air with a diameter of less than 2.5 micrometres -- level was recorded at 326 around 8:20 am, according to data from SAFAR.
An AQI between 0 and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.
While the monitoring station at Mundka recorded the air quality index at 381, which falls in the lower end of the "very poor" category, Anand Vihar recorded AQI of 350, Wazirpur 344, Jahangirpuri 339, Rohini 346, Dwarka sector eight 331 and Bawana 363.
The Ministry of Earth Sciences' air quality forecast and research service, SAFAR, said, "The overall air quality of Delhi is in the 'very poor' category. The decrease in wind speed has started to negatively influence Delhi's air quality by drastically decreasing ventilation coefficients and thereby effecting dispersion."
"The fire count in northern India has reduced slightly but is still moderate at 700. However, winds in the boundary layer, where biomass intrusion takes place, are not quite favourable to influence Delhi's air quality significantly for the next two days."
Calm surface winds will continue for the next two days. Consequently, the AQI is predicted to oscillate between high and middle range of the "very poor" category, it said.
The System of Air Quality and Weather Forecasting and Research (SAFAR) said another western disturbance is likely to affect the western Himalayan region by October 28. In view of this, the situation on Diwali may not be as bad as last year.
The AQI of five places in and around Delhi has been provided in the table given below.