Delhi’s air quality deteriorated sharply on Sunday, plunging deeper into the “severe” category and marking the national capital’s most polluted January day in the last two years. It was also the worst air recorded in the latter half of January since 2019, a period that is typically less polluted than the first half of the month.
According to the Central Pollution Control Board’s (CPCB) daily bulletin, the city’s average air quality index (AQI) stood at 440 at 4 pm on Sunday. This was a significant jump from Saturday, when levels had already crossed the 400-mark, and represented the highest AQI recorded so far this month, apart from the 447 logged on January 14, 2024.
On Monday, the city woke up to fog and ‘severe’ air pollution, with the AQI reading at 418 as per CPCB. The highest reading was recorded at Ashok Vihar station (473). Dense fog also continued to delay flights amid cold wave conditions.
Unusual Spike In The Second Half Of January
Experts flagged the spike as particularly concerning because air quality generally begins to improve in the latter half of January, after peaking earlier in the winter season. Sunday’s reading of 440 was the joint-worst AQI ever recorded during this period, matching the level seen on January 17, 2019.
Data shows that the second-half January AQI peaked at 430 in 2016, when Delhi had fewer monitoring stations. In subsequent years, the highest readings during this period were 375 in 2017, 403 in 2018, 370 in 2020, 407 in 2021, 387 in 2022, 407 in 2023, 409 in 2024 and 368 last year.
This was also the first instance since end-January 2016 that the AQI remained at or above 400 for two consecutive days during the second half of the month.
Scientists attributed the sudden deterioration largely to unfavourable meteorological conditions. Slow surface-level winds, coupled with a western disturbance bringing moisture, created conditions that trapped pollutants close to the ground, leading to a rapid accumulation of emissions.
Grap Stage 4 Curbs Imposed
In response to the worsening air, the Commission for Air Quality Management (CAQM) enforced Stage 4 of the Grap restrictions on Saturday evening, after AQI levels crossed 400 for the first time this year.
Forecasts suggest that a marginal improvement may be possible on Monday, with weather conditions expected to help bring the AQI back into the “very poor” category.
CPCB defines air quality as “moderate” when AQI ranges between 101 and 200, “poor” between 201 and 300, and “very poor” between 301 and 400. Any reading above 400 is classified as “severe”.
Anand Vihar Tops Pollution Charts
Among Delhi’s monitoring stations, Anand Vihar emerged as the most polluted area, recording an AQI of 497 at 12 pm, which was just three points short of the maximum possible reading of 500.
Mundka and Rohini also witnessed extreme pollution levels, each registering an average AQI of 491.
Sunday marked Delhi’s first officially recorded “severe” air day of the year. While AQI levels breached 400 on Saturday, this happened only at 5 pm, an hour after the official daily reading is taken. The last time the city saw “severe” air was on December 29, when the AQI stood at 401.
It was also the second-worst air day of the current winter season, surpassed only by December 14, when the AQI had climbed to 461.
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