Back in Christmas 2013, the CineStar cinema in Mainz, Germany, became an impromptu, oversized laboratory. Over the course of 108 screenings of 16 films, it hosted an unprecedented experiment on about 9500 moviegoers. Not that most of them noticed, or even knew they were under scrutiny. Science was likely the last thing on their brains as they flocked to the cinema to see the German hit Buddy or blockbusters such as The Hunger Games: Catching Fire and The Hobbit: the Desolation of Smaug.
But Jonathan Williams, an atmospheric chemist at the Max Planck Institute for Chemistry, whose research has taken him around the world, went to his local cinema in search of a story that wasn’t being shown on a screen. He was looking for a story told by the breath of a crowd. He chose the screening room of a cinema because it’s well contained. “It’s really just a box full of people,” he says.
Breath contains valuable information, if one can figure out how to decode it. When excited, we emit more carbon dioxide. After a swig of beer, we exhale ethanol in proportion to the amount in our blood. Our breath reveals if we’ve recently eaten an apple or smoked a cigarette. A human breath contains on average more than 200 easily measured volatile organic compounds (VOCs) – chemicals that exist in a gaseous state at room temperature. Most of those are inhaled initially, but many are generated by living cells and metabolic processes in the body. Not every breath is identical: researchers have identified thousands of individual chemicals that fluctuate depending on where people are, what they’re doing, and how their bodies work. A VOC may be innocuous or harmful; natural or synthesized.
“The breath is basically garbage,” says Joachim Pleil, an analytical chemist with the US Environmental Protection Agency at Research Triangle Park in North Carolina, US, and editor-in-chief of the Journal of Breath Research. “You breathe it out, you ignore it.”
Read more about the secrets of breath in my Physics World cover story, here.