After a brief respite, Delhi's air quality deteriorated again to 'very poor' category on Friday as a dispersion of pollutants slowed down, authorities said.
The overall air quality index was recorded at 315 which falls in 'very poor' category, according to the Centre-run System of Air Quality and Weather Forecasting (SAFAR).
Sixteen areas recorded 'very poor' air quality, 22 areas in Delhi recorded 'poor' air quality while seven areas recorded 'moderate' air quality, according to data by the Central Pollution Control Board.
On Friday, the PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) level was recorded at 139, while the PM10 (particles in the air with a diameter of less than 10 micrometres) was recorded at 210 in Delhi.
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'.
Delhi's air quality has shown significant improvement in the past two days after rain washed away the pollutants.
But as the rain subsided, a rise in pollution level was again recorded on Friday, authorities said.
According to the Indian Institute of Tropical Meteorology, fire counts observed in past 24 hours over the northwest region of India were few (less than 100 counts).
"The impact of biomass burning in northwest India is not significant over Delhi," it said.
The PM2.5 concentration will improve in the next two days. "The air quality is likely to improve the next two days but remain in 'poor'/'very poor' category in Delhi-NCR. The impact of biomass burning in northwest India is marginal over Delhi," it said.
