The air quality in the national capital remained 'poor' on Tuesday, largely due to wind direction that changed to northwesterly on Sunday, increasing the contribution of smoke from stubble burning in neighbouring states to pollution in the city.
Westerly and northwesterly winds bring dust from western regions and smoke caused by burning of crop residue in the neighbouring Punjab and Haryana to Delhi-NCR.
After fluctuating between "poor" and "very poor" for over a week, the city's air quality had improved to "moderate" category on Saturday, mainly due to a squall in Delhi that dispersed pollutants and rainfall in neighbouring areas that subdued the effect of stubble burning. According to the System of Air Quality and Weather Forecasting and Research (SAFAR), the overall air quality for Delhi was recorded in the 'poor' category on Tuesday for the third day in a row since then.
The PM2.5 -- particles in the air with a diameter of less than 2.5 micrometres -- level was recorded at 250 around 9 am, according to data from SAFAR.
Region-wise, air quality was recorded as as 'very poor' in Chandani Chowk and Noida. The air quality in Mathura Road region was recorded in higher end of 'poor' category.
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'.