Barely a day after Delhi-NCR breathed slightly better air, an overnight change in the wind direction led to its pollution levels and pollutants rising 10 times over the prescribed safe limits.
The air-quality index touched 426 on Monday, falling yet again in the 'severe' category. Delhiites complained of breathlessness, irritation in their eyes due to the rise in PM2.5 pollutants, dampening the start of Diwali week. Early on Monday, spots such as Anand Vihar recorded PM10 levels of 1,017 micrograms/metre cube — more than 10 times the safe limit.
On Sunday evening, Delhi's skies bore no sign of severe pollution as strong winds had swept away the toxic pollutants. However, an overnight change in winds — from easterly to northerly and northwesterly — was the chief reason behind the plunge in air quality.
Meteorologists and government scientists said that the change in wind directions triggered incursion of smoke generated from the burning of paddy straw in Punjab and Haryana.
Combined with the incursion of extra moisture, the air had a larger capacity to hold on to pollutants, leading to the smoggy conditions.
A departing western disturbance, a weather system that brings icy, moisture laden winds from the Mediterranean, brought in the extra moisture and cool winds that also led to a drop in the temperature in Delhi.
Scientists from the Indian Institute of Tropical Meteorology said that even as air quality may improve marginally, pollutants will continue to be many levels above safe limits. "Surface winds are coming predominantly from northwest direction with wind speed of 5 kmph and is likely to be northwesterly till Wednesday," the government's air-quality forecast said.
