In late 2018, as smoke from the Camp Fire engulfed the Bay Area for days on end, Nina Lewis bought a PurpleAir sensor. For about $250, the small WiFi-equipped air pollution monitor allowed her to track the air quality index, or AQI, as well as particulate matter levels in real time outside her home near San Mateo, California.
Compared to readings from the closest government air monitor nine miles away, the sensor gave Lewis a clearer picture of how much pollution was affecting her local surroundings, informing her about things like whether to wash the car or take the dog for a walk. She thought her neighbors might also appreciate that data, which populates a free public map of global PurpleAir sensors. But she didn’t realize how dependent others had become until the day her husband unplugged the device to mow the lawn.
“A guy popped up on Nextdoor, asking me what had happened to the PurpleAir monitor,” said Lewis, who works as a computer security manager at Oracle. “It turned out people were looking.”