PurpleAir collects measurements of PM2.5 concentrations from a public network of sensors that continuously monitor air quality. Real-time data are transmitted to PurpleAir servers where they are aggre
*From Ambient Air Quality Standards (GB 3095–2012) and Technical Regulation on Ambient Air Quality Index (HJ 633–2012, on trial) from the website of the Ministry of Environmental Protection, China (ht
