This December, Kolkata breathed its cleanest air in recent memory

KOLKATA: The city is witnessing the cleanest Dec in recent years, thanks to favourable climatic conditions and proactive ground-level action to contain pollution. Significantly, this is the first Dec when Graded Response Action Plan (GRAP), an emergency response mechanism to address deteriorating air quality, has been introduced. It kicks in the moment air quality index turns 'poor'.

An analysis of Central Pollution Control Board's Dec AQI calendar for Kolkata over the past five years reveals that the number of 'moderate' AQI (101-200) days increased in 2024, but 'poor' (201-300) and 'very poor' (301-400) days decreased drastically. In fact, Dec 2024 does not have a single 'very poor' day yet. Even Ballygunge, which was the worst among the city's seven air quality monitoring station this month with 12 'poor' days, did not have a single 'very poor' day. In 2023, there was one 'very poor' day in Dec, but in 2022 there were 20. In 2020, there was even one 'severe' AQI day (401-500).

Before 2019, 'severe' days were not very uncommon in the city, leaving it competing with the AQI in Delhi on some days in Dec and Jan. In December 2020, the RBU (BT Road) station recorded 27 'very poor' days. The better figures in recent years show targeted containment measures have paid rich dividends, say experts.
‘Need air-shed approach to tackle pollution in Kolkata’

Unusual warmth, steady breeze that dispersed particulate matter, intermittent drizzle and strict measures adopted by the state Pollution Control Board and Kolkata Municipal Corporation (KMC), among other factors have kept pollution in check this month.

“It was a result of a combination of efforts – getting air quality data, analysing them, taking help from premier research institutions, issuing targeted and region-specific regulatory guidelines and their exact implementation,” said WBPCB chairman, Kaly an Rudra. “We needed a robust source-apportionment study of air pollution in the city to identify the sources and the magnitude of their contribution. Once this was completed in 2019 by National Environmental Engineering and Research Institute after a four-season study, we had a fair idea about the sources, and our measures were very targeted. We are now introducing green chullahs for urban and rural poor,” he added.

In winter, degradation in Kolkata’s air quality is largely driven by PM2.5 or finer particulate matter that directly reached the lungs. “Since the spike in PM2.5 happens due to any smoke, road dust resuspension and construction activities, we, along with KMC started targeting these,” added Rudra.

Experts say the challenge now is to reduce ‘moderate’ AQI days and increase the number of ‘satisfactory’days, but warn that this may not be achieved unless we shift from a city-based pollution control regime to an ‘airshed’ approach. Kolkata, being at the tail-end of the IndoGangetic Plain, often gets a big proportion of trans-border pollution, finds a Delhi IIT study.