With higher temperatures, Capital logs second-best Feb air since 2016

Delhi receives an average of 21mm rain in February, but this past month, no western disturbance influenced the National Capital Region, leading to the city witnessing no rain

Despite receiving no rain in the entirety of February, Delhi recorded its second-best air quality for the month in eight years, data from the Central Pollution Control Board (CPCB) has shown. However, the city logged no good or satisfactory air days in the month, showing that considerable improvement is still required, officials said.

A sunny day at Kartavya Path in New Delhi on February 21. (HT Archive)

Delhi receives an average of 21mm rain in February, but this past month, no western disturbance influenced the National Capital Region, leading to the city witnessing no rain — and higher-than-normal temperatures.

According to CPCB data, the Capital logged an average Air Quality Index (AQI) of 237 this February — the second-best AQI that Delhi has logged since 2016 (the CPCB started measuring Delhi’s AQI from April 2015). The only year when Delhi’s pollution levels were lower in February was in 2022 — an average AQI of 224 — when the city received 29.7mmrain. In contrast, the city’s average AQI for February 2021 was 288.

Experts said this year, a combination of strong winds and an early rise in temperatures likely helped in the dispersal of pollutants. “In the first half of the month, we had strong winds on most days... The stronger the wind speed, the faster is the dispersal of pollutants and gases,” said Kuldeep Srivastava, scientist at India Meteorological Department (IMD).

According to experts, a good spell of rain can bring down dust and other pollutants for several hours, making for a relatively cleaner air day than normal. In such a scenario, gases emerge as the city’s lead pollutant.

Srivastava said though the Capital received no rain this February, the month was largely characterised by above-normal temperatures. “High temperatures lead to a high mixing height, which is a layer of the atmosphere within which pollutants get trapped. In winters, due to low temperatures, this can be as low as 500 to 1000 metres, while in the summers, due to the high temperatures, it can be over 3000 or 4000 metres,” he said.

Another IMD official, on condition of anonymity, said that February may be thought of as a spring month, but the Met department officially classifies it as part of winter. However, the official noted, this year, the average monthly maximum was 27.7 degrees Celsius (°C) — 3.5 degrees higher than the monthly normal average of 24.2°C, making this Delhi’s warmest February since 2006.

“Normally, February is a lot cooler, particularly at night. Low temperatures generally lead to stagnation and calm wind conditions,” the official said.

Srivastava also said that the high pollution levels this year was more down to local factors and not due to factors such as the long-range transport of dust from Rajasthan, which is generally associated with the summer months.

Meanwhile, this February, Delhi’s lowest AQI was just 132 on February 14, with no good or satisfactory air days recorded. In contrast, the city saw one satisfactory air day in 2022, when the AQI fell to 92 on February 17.

On the flipside, the city logged no severe air days this February, and the highest AQI for the month was 371 on February 18. This was lower than the worst air day in 2022, when the highest AQI logged was 346 on February 1.

SN Tripathi, professor at IIT Kanpur who is part of the steering committee of the National Clean Air Programme, said meteorological factors helped Delhi with its pollution levels this February. “Temperatures were higher than normal, but had they been slightly higher — for instance 35-40°C — then we may have seen a greater impact of dust pollution. That generally tends to happen in April or May, when the soil has barely any moisture left. Under the present scenario, there was some impact of local dust, but good wind speed helped,” he said.

CAQM lifts Grap Stage 2 curbs

After three days of air in the “poor” zone, Delhi’s pollution levels improved to 178 (moderate) on Wednesday, prompting the Commission for Air Quality Management (CAQM) to lift all curbs under Stage 2 of the Graded Response Action Plan (Grap) with immediate effect.

The decision lifts the ban on diesel generator sets across NCR, with the use of coal and firewood, including its usage in tandoors at hotels, restaurants and open eateries, also allowed.

“Since February 26, 2023, Delhi’s overall air quality has significantly improved from a reading of 291 to 178 which was recorded as per the 4PM AQI Bulletin provided by the Central Pollution Control Board (CPCB) on Wednesday. In view of this improvement in the overall AQI of Delhi over past few days and also considering the meteorological and weather forecasts by IMD and the Indian Institute of Tropical Meteorology, the Sub-Committee for invoking actions under GRAP feels it is advisable to relax the ongoing restrictions under Stage-II of GRAP and roll it back with immediate effect in the entire NCR,” said CAQM in a statement on Wednesday.

Stage 2 measures under Grap had come into force from October 19, 2022 before the curbs were lifted on February 1 this year, when Delhi’s AQI improved considerably. However, following a deterioration of the city’s pollution levels to the “poor” and “very poor” zones, Stage 2 restrictions were re-imposed on February 16.