Bogotá Cyclists Built a $100 Sensor to Prove the Bus Was Worse Than the Street

CanAirIO is an open-source citizen-science project that began in Bogotá in 2017, when software engineer Alvaro Vanegas teamed up with activist Daniel Bernal, who was already tracking pollution with homemade sensors. Anyone can build a PM2.5 monitor in a few hours for roughly 50 to 100 US dollars, compared with 30,000 to 100,000 dollars for an official station, and then log air quality from a phone while moving or from a fixed WiFi station. Data from the network pointed to ageing diesel buses as a hotspot, with cabin air up to ten times worse than other parts of the city, and the team has trained students as young as 12 to build and deploy the devices. The firmware, Android app and build guides are all free and still actively updated, with commits as recently as October 2026.