NEW DELHI: Air quality in the national capital entered the "very poor" category for the first time this season on Tuesday due to unfavourable conditions for dispersion of pollutants, authorities said.
Stubble burning accounted for six per cent of PM2.5 pollution in Delhi.
The rest of the pollution is due to local sources, said Gufran Beig, the founder project director of SAFAR, a government framework for air quality forecasts.
According to the Central Pollution Control Board, the capital recorded a 24-hour average air quality index (AQI) of 303.
It was 281 on Monday, 289 on Sunday and 268 on Saturday.
The neighbouring cities of Faridabad (306), Ghaziabad (334), and Noida (303) also recorded very poor air quality.
An AQI between zero 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".
"It is (very poor air quality) a result of accumulation of pollution from local sources due to low temperature and low mixing height, Beig said.
Mixing height is the vertical height in which pollutants are suspended in the air.
It reduces on cold days with calm wind speed.
Delhi did not record even a single day of "very poor" or "severe air quality" in October as an extended monsoon season and western disturbances led to record-breaking rainfall in the month.