By Subir Bhaumik
BBC News, Calcutta
Auto rickshaws are some of the worst pollution offenders
For five days, millions of people in the Indian city of Calcutta have endured long queues in the stifling heat at bus and taxi stands, metro railway counters and on auto-rickshaw routes.
They are braving both the humidity and the rain in the hope that what has been termed the city's "great transport mess" will finally be cleared up.
While the difficulties of getting from A to B may be greater now than at any time over the last two decades, the air of the city is much cleaner than before 1 August.
That was when police started seizing all pollution-emitting pre-1993 vehicles to ensure they are kept off the roads in keeping with a Calcutta High Court order.
A survey done by the Calcutta-based Saviour and Friend of Environment (Safe) says that around the city's four most polluted intersections - the Dunlop crossing, the Shyambazar five-point crossing, Park Circus and the Rashbehari Avenue-SP Mukherjee Road crossing - hydrocarbon levels more than halved.
Auto-rickshaw drivers have tried to keep public transport off the roads
That is important because high hydrocarbon levels have been blamed for an increase in liver and kidney illnesses as well as higher level of cancer.
With less traffic on the roads, the oxygen count shot up by around 15 to 20%, leading to a drop in the percentages of carbon dioxide and carbon monoxide.
Suspended particulate matter, the main cause of bronchial diseases that makes Calcutta the asthma capital of India, dropped by 50%.
"Calcutta is back to low pollution levels it enjoyed until about 20 years ago," said Safe's convenor, Sudipto Bhattacharya.
"The vigil has to continue and none of the 15-year-old vehicles or those older should be allowed to go back on to the streets."
Mr Bhattacharya said that Safe's findings vindicated the green activists' stand against older vehicles.
Many other fresh air fans agree with him.
"The sharp drop in the hydrocarbon level proves that older vehicles are the major culprits," said green activist Subhas Datta, who lobbied the city's high court to seek the withdrawal of all vehicles older than 15 years.
"They emit unburnt fuel into the air that pushes up the hydrocarbon level to dangerous levels. Let us hope that Calcutta will breathe freely from now on."
But some of the worst polluting vehicles, especially the two-stroke petrol engine auto-rickshaws, are still plying the Calcutta suburbs because police surveillance is mainly focussed on the core metropolitan area between the main airport in the north and Garia in the south - and from the Kidderpore-Behala arc in the west to the Eastern Metropolitan Bypass.
Owners of old vehicles are upset by the ban
Many of these old and dilapidated machines have been getting a fresh coat of paint to fool the police into thinking they are less antiquated than they are.
In some painting workshops of the city, two-stroke autos are being painted green to mislead the authorities that they are running on liquefied petroleum gas (LPG).
"But that is not the case," admits Radheshyam Das, a paint workshop owner.
"They have not converted to gas, they are taking the new paint only to bamboozle the police.
"But I cannot refuse to paint them because I am not the right authority to check what fuel the auto is running, I am just supposed to paint them."
Many of the autos coming into the paint workshops are the worst offending pre-2000 two-strokes, which have been banned by the high court.
A few are "dual mode" - able to run on petrol but also fitted with an LPG kit.
These too have been prohibited, as the government will allow only single-mode LPG autos that have no chance of ever running on petrol or diesel again.
Police say that spotting auto-rickshaws breaking the rules by having a green paint makeover presents a challenge.
"But we have prepared a detailed list of the older vehicles and that has been circulated to the police, so continuing to fool the police won't be easy," says West Bengal government's transport secretary, Sumantra Chowdhury.
Nearly 4,000 private buses, 6,800 taxis and more than 95% of the total fleet of 65,000 auto-rickshaws have been barred from operating in the Calcutta Metropolitan Area following the Calcutta High Court order.
The ban affects thousands of taxis, mini-buses and auto-rickshaws.
Those laid off work as a result of the ban, especially the auto rickshaw owners, have been trying to prevent the "green" autos from running. That has made life difficult for Calcutta's five million commuters.
"But I would rather stand in long queues for a bus or a green auto than patronise these polluting vehicles again," says Sudeshna Majumder, a school teacher who changes transport three times - using an auto rickshaw, a bus and a suburban train - to reach her school in western Calcutta.
So for the time being it seems as if the city's hard-pressed commuters are broadly in support of the government. They may not have the transport they require but they do have clean air.
It would seem that there is a silver lining behind the city's poisoned clouds.