Meet Dyson’s “air pollution detectives”
1. RUBBER — Rubber can come from different sources — you might

get rubber from car tyres in the filter, but the presence of rubber doesn’t automatically mean the air purifier was in the city, it’s just as possible that the owner was a keen runner, as trainers can also produce rubber particles like this. 2. COOKING OILS — The presence of oil particles shows that the filter probably comes from a device that was located in a kitchen. The concentrations of oil can indicate whether the user was a fan of a regular fry-up, or only cooked with oil occasionally, while further analysis could probably tell you whether they favoured olive oil or sunflower oil. 3. TAR DEPOSITS — If a house were surrounded by dirt tracks, you’d be less likely to find tar deposits on a filter so this generally indicates an urban environment. Hotter climates can mean more tar is likely to be picked up from the roads outside so you might expect to find a higher concentration of tar on the filter.

This isn’t just professional nosiness. “If we can get a better idea of the sort of pollutants that our customers are exposed to, and can understand the different problems in different environments, we can ensure we’re creating products that best serve the needs of the people using them,” says Gem whose work focuses on the small particles — everything from plastic to pollen — found in HEPA filters.

Before you can begin to identify a particle, you have to be able to see it, and to do that these detectives use Scanning Electron Microscopy (SEM), an imaging technology many times more powerful than your average magnifying glass.

“We fire electrons at the surface of something and when they bounce off it, we pick up the pattern that the scattered electrons make to create a 3D image of the particle that we’re looking at,” explains Gem.

To analyse an entire filter in this way would take weeks. Instead, the scientists take representative samples from different areas of the filter. Even then the process can still take several days. “I recently spent three days having ‘a quick look’ at a filter,” laughs Gem.

Sometimes it’s apparent just from looking at the particle exactly what it is — a grain of pollen, for example, has a very characteristic shape. But at other times, chemical analysis is needed.

“At first glance, an organic particle and a rubber particle can look similar,” says Gem.

And while some particles might be easier to identify than others, to date, they’ve not stumbled across anything that’s been a total mystery.

“You might need to do more tests, or look into more literature, but you normally figure it out eventually.”
['Dyson On']
['Engineering', 'Air Pollution', 'Health', 'Dyson', 'Environment']