Delhi's air quality goes further down, reduced wind speed cited as a reason

Delhi's air quality deteriorated further on Thursday - to severe category due to reduced wind speed that prevented the dispersion of pollutants, authorities said. According to Central Pollution Control Board data, the overall air quality index (AQI) in the city was 443, which falls in the severe category. An AQI between 100 and 200 comes under the moderate category, 201 and 300 is considered 'poor', 301 and 400 'very poor', while that between 401 and 500 is 'severe'. The air quality was 'severe' till Sunday but increased wind speed of 20 km/hr significantly improved it, to the poor category, on Tuesday. On Wednesday, the air quality again deteriorated as the wind speed dropped and was recorded in the very poor category. On Thursday, as many as 31 areas recorded 'severe' air quality and two 'very poor' air quality, CPCB said.

In the National Capital Region, Ghaziabad, Faridabad, Noida and Greater Noida recorded 'severe' air quality while Gurgaon recorded 'very poor' air quality, it said. The overall PM2.5 level — fine particulate matters in the air with a diameter of less than 2.5 micrometers - in Delhi was 345, while the PM10 level was 513, it said. The Centre-run System of Air Quality and Weather Forecasting (SAFAR) said air quality index over Delhi touched the "severe" category. "Both the components of particulate matters viz. PM2.5 and PM10 touched severe level. In all probability, the AQI is expected to go up further within severe range until Friday," SAFAR said. "Although there is no appreciable change in wind speed since yesterday (Wednesday) but pollution is getting accumulated mainly because even during day time (Thursday), boundary layer height is very low which normally remains up as sun rises and relative humidity is almost 100 per cent," SAFAR said. "An intense western disturbance along with induced cyclonic circulation is another reason affecting north Indian region and may impact Delhi by Friday. Declining trend is expected from Friday evening and relief is expected only from Saturday when temperature is expected to increase," it said.

(With inputs from agencies.)