Apart from the occasional blast of fumes so strong it left an acrid, industrial taste for a few fleeting seconds, there was little to suggest there was anything unusual about the air.
But, as crowds of people made their way to work on London Bridge on a breezy spring morning, they passed through clouds of exhaust fumes that could eventually make them one of the tens of thousands of people whose lives are brought to a premature end by air pollution every year in the UK.
If only there was a way to make them see the invisible poison all around them, there might be a greater demand for something to be done.
The sensor in the camera took seven minutes to cool down to its operating temperature of minus 176 degrees Celsius. The FLIR GF343 infrared camera is designed to detect leaks of carbon dioxide, mainly in industrial processes.
However, as exhaust fumes are rich in carbon dioxide as well as pollutants harmful to human health, such as fine particles, ozone and nitrogen oxides, the camera can effectively render the invisible visible.
A stream of cyclists moving up towards a cycle lane passed to the left of a near-stationary bus, well away from the exhaust on the other side.
But the camera showed the stream of fumes was being blown across the road before ballooning up into their faces. Some wore face masks, but most did not.
Buses and lorries produced by far the most fumes, but a few buses appeared to emit little more than some of the cars.
Our inability to see most exhaust fumes has also been exploited by carmakers. Few vehicles had a visible exhaust pipe, presumably a design aimed at exploiting the human tendency towards ‘out of sight, out of mind’.
But the infrared images of the camera gave each passing car a flaming tail. A second imaging technique extrapolated the flow of fumes to give a more comprehensive picture of where it was going.
It came as a shock to some of the passersby, even a student from Chinese capital Beijing, which is infamous for its polluted air, who was waiting at a bus stop near the south side of the bridge.
After viewing the images, Xian Shi, 22, who is studying banking and finance in London, said: “I think it was more than what I expected. I never think about that [air pollution] so much.”
Asked to compare London to Beijing, she said: “It’s better here. It depends, in Beijing in summer it’s quite good, but maybe in winter or late autumn it’s not good.”
She was not alone in being taken aback by the film.
Richard, 33, a pipe fitter from South London, was born and raised in the city, but said the images showed more pollution than he had expected.
“According to that [the film], it’s quite a lot. You can’t taste it or smell it, so you just become immune to it,” he said.
Richard, who said he preferred not to give his second name, said more could be done to reduce pollution in the city centre.
But he added: “Everyone needs transport to get about and not everyone can afford to change from diesel or petrol to electric [vehicles].”
Economist Srdan Tatomir, 30, originally from Croatia but now living in Bermondsey, was among the cyclists to pass through the clouds of bus exhausts.
Of the three, he was the only one not to be surprised by the film.
“When I’m pulling up on the bridge, going uphill, and a bus is accelerating … you feel it. Lorries are usually quite bad, a lot of exhaust fumes,” he said.
“It’s quite noticeable. I don’t know what the long-term effect is … but it’s not helpful.”
But would it make him give up cycling?
“No, not so much. I lived in Holland and they cycle no matter what. But I have been wondering about the indirect effects. It’s been on my mind,” Mr Tatomir said.
“I see this on a daily basis. It isn’t that shocking to me.”
Andreas Zinssmeister, business development manager at FLIR Systems, said the camera could be an eye-opener for some.
“Our technology is designed and built to visualise gases. Used across various industries, this particular camera (GF343) can also be used to help spread awareness of fume levels in busy city areas,” he said.
“By visualising this for commuters, it can help make people think twice about their exposure to car fumes when traveling across busy areas.”
Air pollution has recently forced its way onto the Government’s agenda, but does not appear to be particularly high.
It has been successfully sued twice by environmental lawyers at campaign group ClientEarth because its air quality plans have not been good enough to comply with European Union regulations.
The Department for Environment, Food and Rural Affairs is currently preparing its third attempt to get it right.
A Government spokesperson said it was "firmly committed to improving the UK’s air quality and cutting harmful emissions".
"That’s why we have committed more than £2bn since 2011 to increase the uptake of ultra-low emissions vehicles and support greener transport schemes and set out how we will improve air quality through a new programme of Clean Air Zones," the spokesperson said.
"In addition, in the Autumn Statement, we announced a further £290m to support electric vehicles, low emission buses and taxis, and alternative fuels.
“We will update our air quality plans in the spring to further improve the nation’s air quality.”
Greenpeace UK urged the Government to phase out diesel vehicles as part of its air pollution strategy, saying “improving people’s quality of life should be at the top of its agenda”.
Areeba Hamid, clean air campaigner at the campaign group, said: “Imagine how differently we might think of the issue of air pollution if it were visible all around us.
“But of course transport emissions, especially from diesel vehicles, are a largely invisible problem. Visualising these fumes helps us all to understand the extent of the problem – it’s there in our parks, at our bus stops and in our schools.
“But whether we can see them or not, the impact of these harmful emissions is deadly serious.
“Air pollution can contribute to and worsen life-threatening conditions like heart disease and asthma; and ultimately that’s shortening people’s lives.”