Move Aside Delhi, Kolkata May Have Worse Air Pollution

Kolkata is rapidly becoming an even more toxic gas chamber than Delhi, but experts need more data. 

5 min read

This winter, Kolkata seems to be aiming hard for the crown for the most polluted Indian metro city, a dubious pole position currently held by New Delhi.

Kolkata’s air pollution at the end of December was in the same category as that of Delhi at “very poor”, which the Central Pollution Control Board of India says may trigger “respiratory illness on prolonged exposure”. Environmentalists claim that Kolkata’s air pollution is actually worse than that being reflected in official data.

Even official data admits that people in Kolkata had to breathe highly toxic air from December 23 to 31. The Air Quality Index (AQI), an indicator used globally to assess pollution status, of Kolkata was 346 during the period, while it was a shade higher (374) in Delhi.

This is against a good air benchmark of 50 and a safety benchmark of 100.

During the period, air pollution spiked on December 25 and 31 in Kolkata, reaching a ‘severe’ condition, considered the worst status possible; it can adversely affect healthy people and seriously impact those with existing diseases.

Kolkata is rapidly becoming an even more toxic gas chamber than Delhi, but experts need more data. 
A smoggy day in Delhi. (Photo: Reuters)

Why the Difference?

Air pollution index is measured on the basis of dominant pollutant of the area. In Kolkata, the official calculation is based on PM10 measurements (fine particulate) as there is yet no system to measure PM2.5 (ultrafine particulate that causes most health damage by entering into the deepest crevices of lungs) in the state pollution control board-run automatic stations. However, driven by diesel combustion, Kolkata’s PM2.5 level is significantly high. It seems that US consulate data, calculated on basis of PM2.5 level, reflects that scenario.
Anumita Roy Choudhury, air pollution expert at Centre for Science and Environment

Some time ago, Samuel Kotis, deputy minister counsellor in the US embassy looking after environment and climate change, also highlighted Kolkata’s PM2.5 threat in a meeting.

Delhi, being the national capital, gets more international attention, but Kolkata is not far behind. The US embassy in Delhi and all four of our consulates, including the one in Kolkata, have air quality monitors where we regularly measure PM 2.5. We found that the level of PM 2.5 in Kolkata was greater than that of Delhi on some days during last winter.
Samuel Kotis

Although the state pollution control board tends to underplay the PM2.5 factor, another global report also highlights its significantly high concentration in the city’s air. The report, Global Urban Ambient Air Pollution Database (update 2016), released by World Health Organization (WHO), clearly shows that among Indian metros, air toxicity is increasing most rapidly in Kolkata, including that of PM2.5.

In Kolkata the annual average PM2.5 level increased to 61 micrograms per cubic metre in 2016 from 43 in 2014; it was worse across the Hooghly river in Howrah – 100 micrograms per cubic metre in 2016 from 47 in 2014. The national permissible limit is 40.

We have already decided to set up a few automatic monitoring stations for PM2.5 monitoring.
Kalyan Rudra, chairman of the state pollution control board,
Kolkata is rapidly becoming an even more toxic gas chamber than Delhi, but experts need more data. 
The streets of Kolkata are becoming really toxic. (Photo: iStock)

Living in a Gas Chamber

If overall average pollution during end December had become very poor, the nights were turned into no less than a gas chamber. An analysis of the data released by CPCB found that during midnight to early morning in third and fourth weeks of December, the city’s air was hardly breathable with AQI level often reaching 500 — the farthest point in the scale — against the benchmark of 100. The average pollution index value from midnight to 4 am during the period was 414, an almost 20% rise over the respective 24-hour value.

According to experts, the pollution in winter nights escalates because the pollutants remain trapped close to surface — and human lungs — as the temperature falls. Green activists complain that almost unmonitored movement of thousand of trucks and other commercial vehicles within the city — mostly polluting and having a free run in absence of any pollution monitoring system — add to the rise in pollution at nights.

Even morning walkers are not safe — and advised not to venture out early morning — as the fine particulate level has remained around 4.5 times over highest permissible limit from 4 to 5 a.m. “People walk or run in early morning to burn calories while inhaling fresh air; however doing heightened physical activities in such poor air can actually backfire on health,” opined A. G. Ghoshal, a senior pulmonologist.

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Inaction in Kolkata

But there was no action in Kolkata regarding skyrocketing air pollution. “It’s a fact that the city, especially during winter, turns into a gas chamber during night and even state government and the pollution control board admitted the trend of pollution shoot-up during night hours at the hearing on city’s air pollution in National Green Tribunal. However, the data you are mentioning are extremely revealing and I will soon highlight the same in the tribunal,” Datta told

He said about 50,000 trucks enter the city every night and there is virtually no system to check their pollution. “While Delhi has been showing indications of action, Kolkata is just sitting on the problem,” observed an environment expert conversant with the pollution dynamics of both cities. He declined to be named.

Kolkata is rapidly becoming an even more toxic gas chamber than Delhi, but experts need more data. 
A traffic jam in Delhi. (Photo: Reuters)

No Improvements

Environment experts say Kolkata’s air will become increasingly toxic unless the state government acts fast. “Kolkata is the diesel capital of the world. Though industrial and constructional pollution also contribute, the main reason behind the sharp increase of Kolkata’s key pollutants, both ultra-fine particulate and nitrogen oxides, is the burning of diesel in vehicles, particularly in close to 99% of commercial vehicles. State government should ensure that these vehicles should be converted to compressed natural gas (CNG) like other metro cities as soon as possible,” Roy Choudhury of CSE said.

But that may be still seven to eight years away. “Both central and state governments are responsible for the situation. Successive West Bengal governments have never pursued the matter with the Centre despite being aware that introduction of the CNG was the only way to curb diesel driven automobile pollution,” alleged Datta.

Incidentally the Jagadishpur-Haldia pipeline, which is supposed to bring CNG to the state and city, was among the five conduits GAIL India had planned to build in 2007 to supply CNG across the country. Apart from the Haldia line, all others have been completed. A GAIL official said the Union Cabinet had recently cleared the proposal for laying the pipe and work would start soon. “Once work starts, it is expected to take at least seven-eight years to complete the project,” the official said.

(This piece originally appeared in India Climate Dialogue and has been edited for length. Read the full piece here.)

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