“So, what smells did you pick up?” the smellguide asks. “Wet cement? Beautiful! Mouldy fabric? Nice! Wood? Great!”

Kate McLean offers “smellwalks” through major cities around the world. Visitors and locals lucky enough to catch one of the cosmopolitan researcher’s irregular tours announced on her website will be able to discover urban spaces in a way few others will have done before, by trying to track down as many scents as possible.

“You might have to stick your nose into something, scratch tree bark or actually break leaves,” McLean told participants at a recent smelltour of New York’s Central Park.

McLean advises participants to sniff rather than just breathe, explaining that about 10% of the odourous molecules present will come into contact with their olfactory receptors when they breathe, but double that amount when they sniff.

On her tours she asks participants to describe the smells they detect, “not merely identify them”. During her last smellwalk, McLean says, one participant picked up “the smell of shattered dreams”, to which another responded: “I got that too – it’s the smell of stale beer on the sidewalk.”

A participant in a New York ‘smellwalk’ follows her nose while checking the different scents of the city.

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A graphic designer and PhD candidate in information experience design at the Royal College of Art in London, McLean also creates “smellmaps” of different cities around the world like Glasgow (Scotland), Milan (Italy) and Paris (France).

A smellmap of Amsterdam laid out by Mclean can also be seen at an exhibition in New York’s Cooper Hewitt Smithsonian Design Museum running until October.

McLean says every city has three basic types of smell, starting with the “background smells” that are always present. “In Singapore, for instance, it’s the smell of humid air and spicy street food.”

Then there are temporary smells, such as those from a bakery where bread is being baked, or from traffic during rush hour. And finally, there are fleeting smells.

“One might come from somebody who walks past you. You can spend a lot of time chasing these.”

It’s estimated that humans have the capacity to discriminate between up to one trillion smells. “In order to detect every smell that’s out there, you’d have to live 114,000 years,” McLean says. – dpa