Air ‘severe’ despite improved wind speeds

An unexpected weather phenomenon, which washed off pollutants hanging in the air, along with improved wind speeds, came to Delhi’s rescue once again on Saturday, saving the city from what was supposed to have been a severely polluted day.

Central Pollution Control Board (CPCB) recordings show that the overall air quality index (AQI) of Delhi on Saturday was 407, in the ‘severe’ zone, as against the 460 recorded on Friday.

The India Meteorological Department (IMD) had on Friday forecasted that the air quality of Delhi was on its way to sliding into the ‘severe plus’ or ‘emergency’ levels on Saturday. Even though till 10am on Saturday, Delhi was engulfed in a thick blanket of fog, as the day progressed this fog condensed and melted the pollutants that had accumulated.

VK Soni, head of IMD’s environment monitoring and research centre, said that on Saturday morning the fog cover over Delhi condensed and precipitated, washing the accumulated pollution particles with it.

“Even though dense fog conditions usually leads to a rise in pollution levels, sometimes the fog condenses and precipitates. In simpler words, when the moisture level in the air increases beyond a point, it flushes and clears the atmosphere. The average wind speed during the day was also around 7-8 kmph, which made conducive conditions for the air to clear off,” said Soni.

IMD recordings show this phenomenon more clearly. At 8.30 am the relative humidity, which is essentially the moisture content in the air, was 100%.

Soni said that from Sunday afternoon the wind direction will change from north-westerly to easterly and this will bring further relief for Delhiites.

“There is also a forecast of another western disturbance impacting Delhi. Even though this western disturbance will not bring any rainfall in the plains, it will improve the wind speed in Delhi and the NCR towns, and this will lead to a further improvement in the air,” she added.

Kuldeep Srivastava, head of IMD’s regional weather forecasting centre, said that from 1am to 10am on Saturday, Delhi experienced a prolonged fog spell, which reduced the visibility to zero metres for several hours.

Despite the dense fog, the minimum temperatures in the city rose to 6.6 degrees Celsius, which was only one degree below the season’s normal. The maximum temperature recorded at Safdarjung weather station, which is considered the official recording for the entire city, was 19.1 degrees Celsius.

“On Sunday too, the temperature is expected to remain in the same range. However, after the wind direction changes to easterly, in the next week, the mercury will rise and even reach around 10 degrees Celsius,” Srivastava said.