As smoke from wildfires chokes the West Coast, social media has been flooded with crowdsourced maps providing near-real time updates on just how horrendous the air really is. Much of the data are from relatively inexpensive sensors from a company called PurpleAir. They’ve only been available for the past few years, but they’re already changing everything from government maps of air quality to how communities are watching out for each other — and keeping track of the air they breathe.
Low-cost air quality sensors that measure particle pollution — including dust, soot, and smoke — have only become available to most non-scientists in the past decade or so, experts tell The Verge. As people push back against polluters in their backyards and cope with fire seasons that have grown increasingly dangerous as a result of climate change, PurpleAir sensors and others like them have become more popular, and more powerful.
“The power is not in one individual monitoring their house, but in the individual contributing his data, and another individual, and the municipality, and a scientist,” says Núria Castell, a senior scientist who studies new pollution monitoring technologies at the Norwegian Institute for Air Research (NILU). “We put all this data together and then then we have something,” she says. The resulting high-resolution air quality maps can actually lead to better urban planning and cleaner air when it comes to pollution from fires, industry, or other sources.
In fact, PurpleAir got its start because of a dust problem. Every day, Adrian Dybwad watched dust from a gravel mine sweep downhill and settle just below his home not far from Salt Lake City, Utah. As the mining company made plans to expand, Dybwad wanted to know how much the dust affected air quality. But there weren’t any pollution sensors nearby, and he couldn’t find one on the market that could do the job and didn’t cost thousands of dollars.
So in 2015, Dybwad, who has a background in surface-mount electronics and computer programming and networking, set out to build his own. The endeavor grew into PurpleAir: a network of more than 9,700 low-cost air quality sensors that feed data into a near-real time global map of air pollution. For the first time this year, the US Environmental Protection Agency and US Forest Service included data from PurpleAir sensors into its AirNow fire and smoke map.
PurpleAir’s sensors cost less than $280 dollars — not exactly cheap, but still well below what someone would probably pay for a new smartphone. Compared to the heavy-duty equipment that researchers typically use to measure air quality, it’s a steal — those models can cost up to $50,000.
That huge range in cost reflects differences in how each air quality sensor is built and operated. High-cost, high-accuracy sensors are typically carefully calibrated, bigger, and use up more energy. Some of these sensors collect particles on a filter and then shine beta rays through them to measure mass. Those types of sensors might require a permit to operate, since the beta rays are emitted from some kind of radioactive source, according to Anthony Wexler, who directs the Air Quality Research Center at the University of California, Davis. Other sensors have very small, fine glass fibers with filters on the end that vibrate almost like a tuning fork, Wexler says. The vibration changes with the mass of the particles collected. And then there’s a slower, more old-fashioned way of monitoring particle pollution by weighing particles captured on a filter in a lab.
PurpleAir’s sensors measure particulates using laser particle counters. “You basically shine a laser through the air and then the particles in the air reflect the light and the detector picks up those reflections,” Dybwad explains. The method is called “light scattering,” and when Dywbad set out to make his first sensor in 2015, the technology to do this was becoming smaller and more affordable.
Around that time, citizen scientists in Stuttgart, Germany were also coming up with ways to take air quality monitoring into their own hands. After meeting in the basement of their city library, Ensia reported in 2017, the group developed a user manual for DIY sensors. The project called Luftdaten, German for “air data,” quickly spread across Europe and scattered across countries in other parts of the world. In China, pushback against…