Delhi’s air pollution crisis is one of the most talked-about global issues relating to environment and climate change. As a result, a multitude of efforts have been taken to alleviate the smog clouding India’s capital city — from the U.N. taking regular stock of the situation and suggesting steps to control the pollution to the national and local Delhi governments making and implementing policies on the ground — and in the air.

However, the same sense of urgency goes missing when it comes to other Indian cities where the air is equally polluted, and at times even more so. Kolkata, one of the largest Indian metros with a population of more than 14 million, is one such city that has been grappling with severe air pollution in recent times.

According to a 2022 report on global air quality, Kolkata was the second-most polluted city in the world in 2019 when taking the city’s population into account. During Diwali — India’s Festival of Lights — in November 2023 and throughout the winter, Kolkata’s air quality remained hazardous and unhealthy.

Indians celebrate Diwali by burning fireworks, which release hazardous gases into the air. A 2022 study, which assessed air quality over the Indo-Gangetic Plains during the Diwali season, found that sulfur dioxide and pollution from fine particulates known as PM2.5 were the major pollutants produced by burning firecrackers. The study confirmed that emissions from fireworks significantly deteriorate air quality, affecting not just the night of Diwali but also subsequent days.

In late 2023, on Nov. 8, four days prior to Diwali, Kolkata was the third-most polluted city globally after Delhi and Pakistan’s Lahore. Then, on Nov. 11, one day before Diwali, Kolkata’s air was reportedly the most polluted of all Indian metros. By Nov. 13, Kolkata once again ranked second in India, behind Delhi, and it was the fourth-most-polluted city worldwide.

The bad air continued into 2024. According to the SwitchON Foundation, an environmental conservation group based in Kolkata, the city’s average Air Quality Index (AQI) has fluctuated in recent times from moderate to poor. By other standards, air quality in Kolkata can dip into the “very unhealthy” zone. According to AirNow, which uses U.S. Environmental Protection Agency categorizations, air quality is considered “good” if the AQI falls between 0 and 50. An AQI of 51-100 is considered “moderate,” 101-150 is “unhealthy for sensitive groups,” 151-200, noted in red, is regarded as “unhealthy,” and 201-300 as “very unhealthy” and 301 or more as “hazardous.”

SwitchOn data show that Kolkata’s air quality in mid-January fluctuated between 195 and 271 the entire week — which would put it solidly in the purple “very unhealthy” category, according to AirNow’s ratings.

What causes air pollution?

AQI, which is a measurement of air quality in a specific area, is calculated based on the most dominant pollutant during a given period. Air pollution can be caused by a variety of pollutants, including gases, heavy metals, volatile organic substances, toxins and particulate matter suspended in the air. The size of a pollutant matters. Larger particulate matter (PM) such as dust, soot or smoke, are known as PM10, meaning they are 10 micrometers (µm) or less in diameter — just a fraction of the width of a human hair — and they are much more dangerous to human health.

When considering the air quality in Kolkata, PM2.5 is the most prevalent. Due to their small sizes, both types of particulate matter can be breathed deeply into the lungs, potentially leading to various health problems, including heart disease, stroke and respiratory problems. Long-term exposure can result in lung cancer and adverse childbirth outcomes. It’s a key indicator for assessing air pollution impacts, according to the World Health Organization (WHO).

According to a 2017 study published by MDPI, transportation in Kolkata was the major factor behind the city’s air pollution crisis, owing to an abundance of poorly maintained vehicles and the use of petrol fuel.

The issue of vehicular pollution in Kolkata is largely due to the high volume of vehicles that travel daily on just 6% of the available road space. This leads to traffic congestion, which in turn lowers the average speed of vehicles and results in significant vehicular emissions. According to the 2017 paper, “The vehicular population in Kolkata has increased at an annual growth rate of 4%. … The heavy concentration of private motor vehicles has been one of the key reasons for congestion, increased travel times, pollution, and accidents.”

Sasanka Dev, an environmentalist, echoed the same. “We have to impose some kind of control over the usage of diesel-run personal vehicles. Also, at a time when the number of vehicles has increased, enough road has not been built. Kolkata has the highest vehicular density among Indian cities,” Dev, joint secretary of Sabuj Mancha (Green Platform), a joint platform of multiple environmental groups in West Bengal, told Mongabay.

There were reportedly 4.53 million vehicles plying 1,850 kilometers (1,150 miles) of road in Kolkata in 2023, bringing the number of vehicles per kilometer to 2,448. By contrast, despite having more than 10.3 million vehicles, Delhi’s road length totals 33,198 km (20,628 mi) resulting in vehicular density of less than 400 per km.

A 2020 media report, stating West Bengal’s transport department records, revealed that more than 3.3 million vehicles in Kolkata and the surrounding area were run on diesel. The Centre for Science and Environment (CSE) had previously called Kolkata the “diesel capital” of the world, with diesel constituting 45% of total oil consumption by car users in the city. The CSE reported noted that 65% of new cars in Kolkata were diesel, as were 99% of commercial vehicles in the city.

CSE warned that black carbon emissions from diesel-run vehicles, with higher carbon content than vehicles run by petrol, were “several times more heat trapping than CO₂”. According to the report, “Diesel cars emit seven times more particulates and five times more Nox [nitrogen oxides] and contribute toward formation of ozone – pollutants of concern in our cities.” Exposure to vehicle exhaust among people in Kolkata and Delhi is 3-4 times higher than the world average, according to the report.

The European Commission had found that the total pollution expenses over the lifespan of a diesel car that is Euro IV compliant — meaning it adheres to standards introduced by the European Commission in 2005 aimed at cutting down emissions, specifically particulate matter — were significantly greater than those of petrol cars, the report further stated. The WHO categorized diesel emissions as a “class 1 carcinogen” for their strong link with lung cancer — ranking in the same class as tobacco smoking.

According to a 2022 study published in the Indian Journal of Medical Research, Kolkata has one of the highest age-adjusted incidence rates (AAR) of lung cancer for Indian cities outsidse the Northeast (where access to medical facilities is lacking). Among males, the incidence rate of lung cancer in Kolkata was 22 in comparison with Delhi’s 11.8, Chennai’s 11.8 and Mumbai’s 9.5. For females, it was 7.0, while the Delhi rate was 4.0. In Chennai and Mumbai, the figure was 4.7 and 6.0, respectively.

Incidences of lung cancer are not just limited to the capital city of Kolkata. A news report in February revealed that lung cancer made up around 14% of all cancer cases in West Bengal, a “worryingly high” rate when compared with the national average of 6%.

Dev, 71, added that even though diesel and petrol prices are now almost at par, a few years ago, diesel was way cheaper. “This led to a massive increase in the number of diesel-run vehicles. As a result, more diesel is burnt and more heat-trapping CO₂ is released, causing air pollution.”

The CSE report suggested that replacing diesel vehicles with CNG was an opportunity to curb air pollution. But the entire state of West Bengal reportedly has only 46 CNG stations, in comparison with Delhi’s 470.

Despite high vehicular intensity, nearly half of the working population in Kolkata commutes by bus, bicycle, train and other transit such as auto rickshaws or taxis. The CSE report found that more than one-fourth of the working population walked to their place of work. But due to the high air pollution, walkers and public transport users — who are part of the solution — are also suffering.

“Kolkata needs a technology leapfrog, scaling up of public transport, integrated multi-modal transport options, car restraints and walking for clean air,” according to Anumita Roychowdhury, CSE executive director, research and advocacy, and the head of the CSE air pollution control campaign.

Consequences of air pollution

The WHO estimates that 4.2 million deaths globally are linked to ambient air pollution, mainly from heart disease, stroke, chronic obstructive pulmonary disease, lung cancer and acute respiratory infections.

A 2020 paper published in International Journal of Environmental Health Research, declared that short-term exposure to pollutants can worsen existing respiratory conditions like asthma, chronic obstructive pulmonary disease (COPD), chronic respiratory sputum, coughing, wheezing and breathing difficulties as well as preexisting cardiovascular diseases such as ischemia, arrhythmias and heart failure. This can lead to an uptick in hospital admissions and visits to the emergency department.

“We don’t have to talk about any illnesses air pollution causes to understand its seriousness. It’s directly linked with lung cancer and increased mortality. That should be enough to ring the alarm bells now,” Dr. Aloke Gopal Ghoshal, a pulmonologist and medical director of the National Allergy Asthma Bronchitis Institute, told Mongabay.

The former WHO Fellow continued, “Extremes of age — that is, children and senior citizens — suffer the most from air pollution. Air pollution causes irreversible damages to a child’s genes. Even if the air quality improves in later years of that person’s [life], the condition of their genes would not improve. We call this epigenetic change.”

Other than its effects on human health, air pollution also has a direct impact on a region’s economy. In India, 1.67 million deaths were caused by air pollution in 2019. (In Kolkata, the 2022 global air quality report found, about 99 deaths per 100,000 people were due to exposure to PM2.5.) According to the findings in a Lancet study, the financial toll of premature deaths and morbidity caused by air pollution in India that year amounted to $28.8 billion (with a range of $21.4 billion to $37.4 billion) and $8.0 billion (with a range of $5.9 billion to $10.3 billion), respectively.

“The high burden of death and disease due to air pollution and its associated substantial adverse economic impact from loss of output could impede India’s aspiration to be a $5 trillion economy by 2024,” the study warned.

Government response

Despite all of this, air pollution in Kolkata does not receive adequate attention from policymakers, Dev said.

“Other than diesel vehicles, waste burning and construction are other important factors behind air pollution in Kolkata,” he said. The CSE report noted the same, saying Kolkata must reduce pollution from all sources, including industrial emissions, waste incineration and dust from construction and roads to effectively clean the air.

“The system of waste processing is nonexistent in Kolkata, the environmentalist said, adding that most waste, dry leaves, wood, etc., are burned in the open, releasing toxins into the air. “At individual levels, citizens of Kolkata also contribute to the city’s air pollution by not managing their waste properly. The government has not done enough to [make people] aware about air pollution,” the environmentalist added.

“Apart from not restricting diesel vehicles, the government has also failed to stop factories and industries that run on thermal and biomass energy in Kolkata and its neighborhood.”

Additionally, the data produced by the existing air quality monitoring system in Kolkata might also be lacking. Kolkata has just seven air quality monitoring stations across the city, while Delhi has 37. Meanwhile, three of the seven stations in Kolkata are located at some of the greenest spots in the city. Consequently, when the data from all seven stations are averaged, the pollution figures may appear more optimistic than the actual situation, reported ThePrint.

The CSE also said that the equipment used for its study registered pollution levels that were higher than the readings taken by the official monitoring devices of the West Bengal Pollution Control Board.

To curb the menace of air pollution in Kolkata and neighboring areas, the West Bengal government’s Department of Environment came up with the “Clean Air Action Plan For Kolkata Metropolitan Area.” The multisector action plan included a variety of strategies across different sectors of air quality monitoring and management, such as “emissions from industry, power plants, vehicles and transportation, municipal solid waste, landfill fires, construction and demolition waste, road dust and open areas, household pollution and episodic pollution like crop residue burning.”

To cut down air pollution resulting from vehicular emissions, the action plan suggested a combination of strategies, including on-road emissions monitoring, phasing out of old vehicles and a range of public transport strategies including walking and cycling.

In addition, the plan called on cities to manage legacy waste through biomining and other techniques to prevent as much waste as possible from ending up in landfills. This included 100% “door to door collection of segregated waste from each household” and “phased reduction of single use plastic.”

Mongabay reached out on multiple occasions to the environment ministry and the West Bengal Pollution Control Board for comment on the implementation status of the 2022 plan and on the air pollution problem in Kolkata. Several emails were also sent to officials of both departments, but Mongabay received no response. The copy will be updated if and when they respond.

Banner image: A road in Kolkata. Image by Shovona Ngela via Flickr (CC BY-ND 2.0).

E-bikes could cut smog, energy use and congestion globally — but will they?