Fog shrouds city; air still 'severe'

Slow winds and an abrupt rise in moisture triggered a thick grey fog across Delhi on Wednesday morning, compounding the city's already severe air pollution.

- Aheli Das

NEW DELHI: The India Meteorological Department (IMD) issued an "orange" alert for Thursday, warning that dense fog conditions may persist for a few more days.

The spectre of pollution, however, continued as Delhi's air fell deeper into the "severe" category - the air quality index (AQI) fell to 445 at 4 pm on Wednesday, compared to 433 ("severe") on Tuesday and 379 ("very poor") on Monday. It continued to rise through the night, and was at 450 at 11 pm.

Scientists attributed the sudden onset of smog to moisture brought in by a western disturbance. The India Meteorological Department (IMD) has issued a "yellow" alert for fog on Friday and Saturday.

According to IMD, the visibility at city's base weather station Safdarjung dropped to 50 metres at 6.30 am, categorised as "very dense" fog. Visibility later improved to 200m by 8.30 am. Palam recorded moderate fog since 5 am, with visibility dropping to 300m at 6.30 am, which persisted till 9 am.

Fog and poor visibility disrupted traffic during peak hours, slowing movement significantly. The Delhi Traffic Police advised commuters to drive cautiously, citing reduced visibility on major roads. The situation was particularly dangerous on highways that connect Delhi to its key satellite towns of Gurugram and Noida.

"Relatively calmer winds were observed over Safdarjung, as compared to Palam, which might have been the reason for lower visibility over Safdarjung. Moderate to dense fog conditions are likely to continue in the morning hours of the next two days," said Krishna Mishra, a scientist at IMD.

IMD classifies visibility between 500m and 1,000m as "shallow", 200m and 500m as "moderate", and 50m and 200m as "dense". Visibility lower than 50 metres is classified as "very dense" fog. The weather office issues green, yellow, orange and red alerts in increasing order of urgency to warn people of unfavourable weather conditions.