How reliable can sensor data be?

How reliable can sensor data be? Commercial pollution monitors are attracting plenty of hype, but scientists say buyers should beware. Tom Marshall explains.

New kinds of smart sensor data are hitting the market, and they could transform how we cope with health risks from polluted air by putting information at our fingertips. Asthmatics could stay indoors when sensors show lots of particle pollution; urbanites might skip their evening jog if nitrogen dioxide levels are high.

There’s just one problem – most of these devices are unreliable and some are practically useless, according to the scientists who tested them. Until manufacturers are more open about the accuracy and limitations of sensors, they’re little more than a curiosity and should not be used to make decisions about health.

“Like many atmospheric scientists I’d heard about these sensors and was rather dismissive,” says Professor Ally Lewis of the University of York, deputy director of NERC’s National Centre for Atmospheric Science. “But we were unsure how well they’d perform, so we started testing them in the lab. The results weren’t very impressive.”

Measuring atmospheric pollution is hard. You often need to find just one molecule of gas in every one billion in air, while managing other factors that could distort the result, like weather or other pollutants. There’s a reason atmospheric chemists and those responsible for meeting legal obligations on pollution use big, high-powered lab equipment and not convenient handheld metres.

Most of the air quality sensors on the market rely on old technology re-purposed from products like fire alarms or car exhaust sensors. Few were designed to monitor air pollution to protect health. “Often it’s not clear what performance people should expect from their sensor,” Lewis says. “Sometimes the marketing does suggest they’re just for fun, but manufacturers can’t control how the data will be used. Ultimately most people are interested in air quality for health reasons – and data from these devices could well be for used for health decision-making and medication.”

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