AQI back to ‘very poor’; Delhi logs rain

Towards the evening, parts of the National Capital Region (NCR) recorded drizzle, heralding a further drop in temperature

Slow wind speeds and low temperatures meant Delhi on Sunday logged its first “very poor” air day of this December, as the Capital’s pollution levels sharply deteriorated after a week of better-than-normal air quality.

Parts of Delhi received a spell of light rain on Sunday evening, snapping a nearly three-month-long dry spell for the Capital. Meanwhile, slow wind speeds and low temperatures meant the city also logged its first ‘very poor’ air day this December, with an AQI of 302. (Arvind Yadav/HT Photo)

Towards the evening, parts of the National Capital Region (NCR) recorded drizzle, heralding a further drop in temperature over the next few days, India Meteorological Department (IMD) said.

Delhi’s minimum temperature was 7.4 degrees Celsius (°C) on Sunday — two notches below normal and marginally higher than the 7.1°C recorded the previous day. This reading was at the Safdarjung observatory, which is the representative for Delhi; however, other parts of the city were even colder, with the Ayanagar station nearly logging cold wave conditions, with a minimum of 6°C — four degrees below the normal.

To be sure, IMD defines a “cold wave” as when the minimum is at least 4.5°C below normal, even as the minimum is below 10°C.

The low temperature, coupled with a drop in wind speed, meant that Delhi’s pollution levels worsened on Sunday, with an air quality index (AQI) reading of 302, according to the Central Pollution Control Board (CPCB) national bulletin at 4pm. This was a severe deterioration from the 233 (poor) logged a previous day.

“Winds were around 5-8km/hr on Saturday and mostly calm at night, which led to a deterioration in AQI. On Sunday, they picked up once again and should remain consistent,” said Mahesh Palawat, vice president at Skymet.

However, by around 6pm, parts of the city recorded drizzle, with an increase in moisture due to a prevailing western disturbance, which is also likely to cause shallow to moderate fog on Monday morning.

The Capital last recorded rain on September 19 (10mm).

“This drizzle occurred in isolated parts of west, south, central and east Delhi,” said an IMD official.

The IMD has forecast a slight increase in the minimum on Monday, before a sharp drop to the 6-degree mark between Tuesday and Thursday.

“Though the wind direction is mostly variable, it will become northwesterly from Tuesday onwards, which is when a further dip in temperature by 1-2°C is expected,” Palawat said, adding that some weather stations may start recording cold wave conditions during this period.

Meanwhile, Delhi’s AQI is forecast to be in the ‘poor’ range on Monday, helped by the rain and a slight increase in wind speed again, before returning back to ‘very poor’ on Tuesday, the Centre’s Early Warning System for Delhi said.

Prior to Sunday, Delhi’s AQI had been hovering between ‘moderate’ and ‘poor’, giving the capital comparatively clean air for this time of the year. The average AQI was 233 on Saturday, 197 on Friday and 165 on Thursday, in what has been a fairly clean start to December.

While most stations in Delhi were in the ‘moderate’ range on Thursday — an AQI below 200 — on Sunday, only the Lodhi Road station (189) was in this category at 4 pm. Out of the 38 stations online, 23 were in ‘very poor’ and had an AQI over 300. The worst was Shadipur (377).

The Commission for Air Quality Management had on Thursday lifted stages 3 and 4 of the Graded Response Action Plan (Grap) with immediate effect, following Supreme Court directions. The top court had also asked CAQM to consider invoking stage 3 of Grap if the AQI touches 350, instead of the current threshold of 400, with stage 4 measures to be invoked at 400 instead of 450.

A CAQM official on Sunday said the body had noted these recommendations and a review meeting will be held if the AQI crosses 350.

Data from last December showed the average AQI was 348, with three “severe” air days recorded. The lowest AQI recorded last year’s December was 286, while the highest was 450 on December 23.

Typically, the second half of December witnesses a spike in pollution levels due to plummeting temperatures, low wind speeds, and the return of dense fog.