New Delhi, October 8: Delhi's air quality has slipped back to "poor" category due to change in direction of wind, which is now flowing from stubble burning areas in Punjab and Haryana, authorities said Monday. The air quality had on Sunday improved to moderate level with an index of 181, but the air quality slipped to poor category Monday with the Air Quality Index (AQI) at 262, says the data at the Centre-run System of Air Quality and Weather Forecasting and Research (SAFAR).

An AQI between 0-50 is considered 'good', 51-100 'satisfactory', 101-200 'moderate', 201-300 'poor', 301-400 'very poor', and 401-500 'severe'.

An official at the Central Pollution Control Board attributed the reason behind the slight improvement on Sunday to less traffic and better wind speed, but as the traffic increased on Monday, the pollution in the city again rose and the air quality fell.

The PM10 level (presence of particles with diameter less than 10 mm) was 242 in Delhi and the PM2.5 level (presence of particles with diameter less than 2.5 mm) in the city was 109, according to data by SAFAR. SAFAR has also forecast further deterioration of air quality in the next two days with the PM10 expected to touch 278 and PM2.5 to reach "very poor" stage at 125 in the next three days.