Over the last 12 days, wildfires have burned more than 1.2 million acres of land in California, an area collectively larger than Delaware. As the smoke pours into cities such as San Francisco, making the air dangerous to breathe, many people aren’t turning to government sites to check the air quality, but to PurpleAir, a tiny startup that maps air quality using sensors in backyards.
Even in large cities, the government typically has only a handful of EPA-certified air quality monitors and updates the readings at most every hour with an hourly average. But the level of pollution can be different even inside the same neighborhood and can quickly change. The PurpleAir map, which is dotted with data from dozens of devices in San Francisco, sometimes shows areas of clean air immediately adjacent to places where smoke is trapped.
“You could say, well, ‘let’s go one block that way, and we might get out of the smoke,'” says PurpleAir founder Adrian Dybwad. “You can tell that if you’re dealing with real-time data. If you’re looking at averages, you might get there and find that it’s changed.”
Dybwad, based in Salt Lake City, started the company as a side project in 2015 because he wanted to better understand the pollution in his own neighborhood, where he could see dust blowing from a gravel mine nearly every day. He experimented with various sensors and settled on a type that uses lasers to measure particles in the air. The light reflects off the particles, and the sensors use that reflection to estimate the size and number of particles. He built monitors that combine the sensors with Wi-Fi to share the data, and he initially gave them away but began selling them as the demand grew. The company, which now has 10 employees, has distributed 1,500 indoor sensors and 7,000 outdoor sensors so far.
The launch of the startup coincided with the growth of megafires in California, where wildfires happen naturally, but climate change has dramatically increased their scale and destructiveness. In the fall of 2015, a major fire in the North Bay destroyed nearly 2,000 buildings. That was followed by another in 2017 that destroyed 5,600 buildings, and a third major fire in 2018 that burned 459,000 acres. In 2018, the Camp Fire destroyed the town of Paradise and blanketed the Bay Area in smoke for days. Two of the fires currently burning are the second and third-largest fires in the state’s recorded history. Major wildfires are also burning in Colorado. As the fires have grown this month, PurpleAir has seen roughly a 1000% increase in traffic to its map.
Each fire poses an immediate threat to life and property; in California, more than 100,000 people have been forced to leave their homes in the current fires, and seven people have died. But the smoke also causes health problems, including heart and lung issues (it may also worsen COVID-19.) Knowing when it’s relatively safe to go outside is key, but the official tools aren’t adequate.
PurpleAir’s data differs from the official air quality readings. One recent study of low-cost air quality monitors, including the PurpleAir, found that the readings were consistent and could be reliable, but they were also higher than the monitors used by the government during a wildfire. That’s because the EPA uses weight, rather than the number of particles, to come up with a number for the air quality index, and wood smoke particles are lighter in weight than something like gravel dust. Dybwad explains that historically, the air quality was measured by weighing a filter before and after it was exposed to polluted air. Now, he says, he’s trying to work within an outdated system. “We’re trying to take a new signal from a new sensor and we’re trying to put noise on it—trying to make a DVD look like a VHS video,” he says.
The PurpleAir map includes the option to convert the readings using two formulas that bring the numbers closer in line to the EPA’s. Dybwad says that he also thinks the EPA may come up with a new scale based on the effects of a certain number of particles of a certain size. “The question now is, are 1,000 particles of wood smoke less harmful than 1,000 particles of the same size of gravel dust? We’ll probably find the answer is no.”
Now, the government is beginning to incorporate PurpleAir data into an experimental new Fire and Smoke Map that also includes data from the official monitors. Unfortunately, it still can’t be viewed in real time. But using data from low-cost sensor networks such as this may be the best way for the government to give citizens more accurate data during wildfires. Dybwad explains that the official government air quality monitors have to be very expensive because they’re used to monitor the effects of regulation over time, and the data has to hold up in court. They weren’t intended to monitor the air during wildfires, and a different solution is needed.
In many cities, that will call for installing monitors in poorer neighborhoods; in Los Angeles, for example, the nonprofit Coalition for Clean Air is giving PurpleAir monitors away to community members. “I think the only sustainable way of managing on a large scale is where the community gets involved in hosting and running sensors like this,” he says.