Delhi's air quality drops to 'poor' with change in wind direction

The national capital's air quality turned "poor" on Sunday as wind direction changed to northwesterly, increasing the contribution of smoke from stubble burning in neighbouring states to the 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.

However on Sunday, pollution levels in Delhi shot up by around 100 points at air quality index (AQI), the Central Pollution Control Board data showed.

The AQI, which was 161 on Saturday, rose to 258 by Sunday afternoon. Higher the AQI of an area, the higher the pollution level.

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'.

The Ministry of Earth Sciences' air quality forecast and research service, SAFAR, said, "The overall air quality of Delhi is back in the poor category. The surface and boundary layer wind direction is northwesterly now."