What Dhaka can learn from Kolkata on cleaning up its air

Just around 300 kilometres apart, Dhaka and Kolkata often top the Air Quality Index (AQI) list as the two cities with the worst air quality in the world. 

For example, on 14 February this year, Kolkata ranked first with AQI scores of 303, while Dhaka was second with scores of 288, based on five pollutants: particulate matter (PM10 and PM2.5), nitrogen dioxide (NO2), carbon monoxide (CO), sulfur dioxide (SO2) and ozone.

However, a recent study by IIT-Delhi's Arun Duggal Centre of Excellence for Research in Climate Change and Air Pollution (CERCA) has painted a completely different picture. It was published on 9 June this year.

It found Kolkata to be the second cleanest city after Chennai among the 11 metropolitan cities in the world in May 2024, as far as PM2.5 concentration in the air is concerned. Dhaka, as usual, came out as the worst city on the list, with Delhi being the second worst.

For the uninitiated, PM2.5 is a major concern worldwide, as it is more likely to travel into and deposit on the surface of the deeper parts of the lung and enter the bloodstream to cause significant respiratory and cardiovascular effects.

The State of Global Air Report 2024 shows that air pollution has become the leading cause of death in Bangladesh, outpacing fatalities from high blood pressure, poor diet and tobacco use. In 2021, at least 236,000 lives were lost in the country due to air pollution. The report also says that 99% of the world's population lives in places with unhealthy levels of PM2.5 (exceeding 35 µg/m3).

According to the CERCA study, Kolkata had a PM2.5 concentration of 18 µg/m³ (microgram per cubic metre) in May, while Dhaka's was a staggering 139 µg/m³. Surprisingly, even cities like London and New York, which generally have a stellar record of containing air pollution, were behind Kolkata on the list, raising many eyebrows.

We reached out to experts and concerned authorities based in India to understand the implication of this study, and how Kolkata's air has become so clean within a few months.

Apparently, Kolkata's recent success, despite how surprising it may seem, was not a fluke. It resulted from a continuous process of numerous government initiatives that can serve as a potential model for Dhaka and other cities in the country to combat the escalating problem of air pollution effectively.

Dr Kalyan Rudra, Chairman of the West Bengal Pollution Control Board (WBPCB), claimed that Kolkata's air quality wasn't even as severe as it was depicted during the winter months. He said relying solely on satellite data for monitoring air quality may not always provide accurate assessments.

He cited a recent World Bank study which explains that even though satellites provide valuable global coverage, they may not reliably estimate ambient concentrations of PM2.5 in low- and middle-income countries (LMICs).

"So, it's not like Kolkata's air quality has suddenly improved," said Dr Rudra, elaborating that several key reasons like temperature inversion, stagnant air, increased fuel and crop residue burning during the winter months (October to March) contribute to the city's poor air quality, as observed in satellite monitoring.

"Meteorology also played a significant role [in Kolkata ranking as the second cleanest city in the world in May]. The heat has elevated the planetary boundary layer, facilitating faster dispersal of pollutants," he explained.

According to Anumita Roy Chowdhury, Executive Director of Research and Advocacy at Centre for Science and Environment (CSE) in New Delhi, the summer in Kolkata in any case is comparatively cleaner than the winter season.

"But this substantial improvement is a combined impact of the Cyclone Remal and the associated storm surge, as well as the clean air action that is underway to meet the target reduction for the particulate matter under the National Clean Air Programme," she said.

And this is where a city like Dhaka can learn a lot from Kolkata.

According to Dr Abhijit Chatterjee, Professor of Chemical Science at Bose Institute, Kolkata, several steps have been taken in three specific sectors to upgrade Kolkata's air quality: biomass burning or solid fuel burning sector, vehicular emissions sector and dust sector.

The West Bengal government has distributed smokeless chulhas to the poor, generated a database on street dwellers and roadside eateries using coal as fuel, and conducted drone-based surveillance over biomass burning and solid waste burning hotspots.

"Efforts have also been made to ensure solid waste segregation at the source, bio-mine legacy waste, and establish a waste treatment plant with a capacity of 500 TPD," informed Dr Chatterjee.

Dr Rudra also weighed in on the fact that all the red category industries that previously existed within the boundaries of Kolkata city have been relocated outside.

Meanwhile, the West Bengal government is prioritising the reduction of vehicular emissions by introducing CNG buses and launching electric vehicles (EVs).

According to Dr Rudra, 60 public buses operated by the West Bengal Transport Corporation (WBTC) in Kolkata are now running on LPG, while approximately 1,800 EVs have been registered so far. The government is increasing EV charging stations to further support this transition.

Efforts are underway to decarbonise old vehicles, with a ban placed on vehicles over 15 years old. "To further improve air quality, air filters are being installed in public buses," stated Dr Chatterjee.

Both Dr Rudra and Dr Chatterjee also highlighted the measures being taken in the "dust sector" (by this we understand industries which produce a lot of dust such as construction sites, coal-powered plants, etc) to curb air pollution. The measures include covering construction sites and the use of mist cannons in them, as well as water sprinkling twice a day on roads and the leaves of roadside trees to minimise airborne particles.

"Also, construction and demolition dust is being recycled in specialised plants to produce tiles and other materials and reduce waste and dust pollution in the process," said Dr Chatterjee.

To minimise transboundary pollution, the WBPCB decided in 2022 to set up a bio-shield — a wall of mega plantations — along its western fringe.

The project aims to cover approximately 800 kilometres (km) across the Purulia, Birbhum, Paschim Bardhaman and Jhargram districts, which are part of the Rarh region and lie on Bengal's border with Bihar, Jharkhand, and Odisha.

Experts suggest that a treaty and coordinated programme with adjoining states and places like Bangladesh could be a more fruitful option to minimise the impact of transboundary pollution.

Another study initiated by WBPCB and conducted by IIT-Delhi in 2021 identified the entry of dust particles from the Bangladesh border as a major source of pollution in West Bengal.

According to the study, 53% of the state's pollution is attributed to transboundary pollution, with Bangladesh contributing 21%.

Dr Rudra emphasised that due to their location at the tail end of the Ganga Basin, pollution levels in the Ganga are notably high, with garbage carried from the source up to the confluence exacerbating the issue. Similarly, dust from the Indo-Gangetic plain easily crosses borders, contributing significantly to air pollution in West Bengal.

So, according to him, it is anticipated that efforts will soon be undertaken to establish a treaty and coordinated program in the future, for the benefit of eight adjoining states with West Bengal, as well as with Bangladesh, Nepal, and Bhutan.

"But in the end, what's most important is raising public awareness about air pollution and its prevention," Dr Rudra concluded.