Study finds high carbon dioxide levels in Mumbai subways

Whenever Nilesh Sharma (60) emerges out of the CST subway to reach CST railway station, he is left gasping for breath. Sharma, who is asthmatic, angrily claims that the subway is more like a “gas chamber”. “Using the subway is a nightmare. When walk the length of the subway, I feel breathless. When I climb the staircase up to the station, I stand and catch my breath before I board a train,” he says.

Many commuters using the subway will empathise with Sharma. After all, at any point, there are a number of people standing at the entrance of Mumbai CST catching their breath. The reason for this breathless has been solved, thanks to a survey conducted by the National Environment Engineering Research Institute (NEERI).

The study

NEERI conducted a survey on the subways at Churchgate and Mumbai CST – two of the busiest pedestrian subways in Mumbai – as part of Talk the Walk campaign. The results reveal that pedestrians are exposed to high amounts of Respirable Suspended Particulate Matter (RSPM or PM10) and carbon dioxide in the subways.

The amount of RSPM and carbon dioxide is three to four times the standard set by the National Ambient Air Quality. Apart from that the study also found that the Carbon dioxide (CO2) levels in the subway too were high during peak hours.

NEERI conducted the survey on March 22 between 2.30pm and 7pm at both subways. The levels of RSPM, CO2, volatile organic compounds, temperature and humidity were studied using various scientific methods. “The readings were taken during the afternoon when there was not too much rush and during evening rush hour,” said Mihir Hirlekar, Project Assistant at NEERI, who conducted the study with three other colleagues.


It was found that Churchgate subway fared better than the one at Mumbai CST. This is despite the fact the CST subway has blowers to pump in fresh air. “It was difficult to work, as we felt suffocated,” said Prasad Khale, who was also part of the study.

Dr Rakesh Kumar, head of NEERI, Mumbai said, “The permissible limit for RSPM is 100 for residential areas and 150 for industrial areas and a high level of RSPM was found in both subways. This can affect pedestrians who have respiratory issues or diseases. Those working long hours in the subway are also affected. There is need to improve the ventilation system so that these issues are resolved in future.”

Shopkeeper woes

There are around 45 shops inside the CST subway (not including encroachments). Each shop has around 5 people, which means there are around 300 people working in the subway, while pedestrians move across.

Mohammed Nazir a shopkeeper who work in one of the shops located inside the subway stated, “The blower installed are of little use as sometimes it just gets unbearable to stay inside the subway as so many of us are forced to come out of the subway and then go back. Many like me regularly complain of headaches and itchy skin but we have no option as we have to earn a livelihood.”

BMC sources agree that the Mumbai CST has some problems. An official said the CST subway’s entrance was narrower compared to the one at Churchgate. “The Churchgate subway is longer, so there are fewer issues compared to CST,” he said.