With a depression likely to form over the Bay of Bengal over the next 24-48 hours, the India Meteorological Department (IMD) has predicted a return of smog and related conditions in Delhi and NCR in the coming week.
Met officials said visibility at the Delhi airport dropped to 500 metres for about four hours on Wednesday — a phenomenon called “radiation fog” — forcing authorities to implement low visibility procedures for flight movement.
“When there is the presence of locally formed moisture, a mainly clear sky and a cool earth surface — which cools by losing solar radiation during night hours — we get radiation fog. It lasted only four hours at the Delhi airport, when visibility dropped to 500 metres between 5 am and 9 am,” Director-in-charge of IGI Met department R K Jenamani said.
The official said a depression was likely to form over the Bay of Bengal in the next 48 hours, which is likely to be succeeded by another system of intensified low pressure. “As a result of the two systems, there are chances of further development of some fog or smog in the Delhi region. “Their further intensification and movement are not ruled out and smog and fog conditions will be critically monitored,” Jenamani said.
The Met department said between October and December, plains in Northwest India and Delhi-NCR, Chandigarh and Lucknow have a highly favourable condition for smog formation due to high levels of pollution and high meteorological wind circulation.
According to data collected since 1989, Delhi witnessed the worst smog conditions in 2012 — between October 28 and November 8. The capital was covered in a thick layer of smoke and haze by the impact of a cyclone which formed over Southwest Bay of Bengal on October 29 that year and crossed the Southeast coast at Karaikal in Tamil Nadu on October 31.
“That smog spell was most unique as it caused a significant reduction in visibility —200-400 metres at night — with some fog mix-up. Even during noon temperatures, the haze/smog persisted. It was so thick that even without fog formation, normal visibility had reduced to 400 metres. Such a long or severe smog spell over Delhi has never been observed since then,” he said.
On Wednesday, humidity was recorded at 86 per cent. Minimum temperatures 17 degree Celsius, two degrees above normal.