Air quality improves by nearly 200 notches

NEW DELHI: Pollution levels in Delhi dropped significantly and the Air Quality Index (AQI), as recorded by the Central Pollution Control Board (CPCB), improved by nearly 200 notches over the past two days, thanks to rain and high-velocity winds that helped disperse pollutants.

Government agencies, however, have forecasted that the pollution levels could rise gradually over the weekend as the wind speed could drop from Saturday. However, the AQI is unlikely to slide back to “very poor” levels.

The AQI, which was recorded at 409 on Tuesday, in the “severe” category, improved to 312 on Wednesday, to the “very poor” category. On Thursday, it improved to 217, to the “poor” category. “The air quality has improved significantly. There was rain for two consecutive nights, the wind speed has picked up and the mixing height — the height to which pollutants can rise and disperse — has also increased. The ventilation index — which determines how fast pollutants can disperse — has also increased, said a scientist from the Indian Institute of Tropical Meteorology, one of the two pollution forecasting agencies in Delhi. Delhi needs a minimum ventilation index of 6,000m2/sec- ond and wind speed of at least 10 km/hour for pollutants to disperse. On Thursday, the wind speed increased to 10km/hr and the ventilation index was around 15,000m2/second. This helped clear pollutants that had accumulated over the past few days.

“The wind speed is expected to increase further on Friday, facilitating more dispersal of pollutants. The AQI will, consequently, improve further,” an IITM scientist said. From Saturday, however, the wind speed is likely to drop as a result of which pollution could start accumulating again.

“We are expecting the pollution to rise marginally from Saturday, as clam winds would be unable to disperse the pollutants,” a CPCB scientist said.