2 ), nitrogen dioxide (NO 2 ), suspended particulates smaller than 10 microns in diameter (PM10), carbon monoxide (CO), ozone (O 3 ), and suspended particulates smaller than 2.5 microns in diameter (PM2.5). The index is employed at monitoring stations in 367 cities across the nation. China’s MEP measures airborne pollution using its Air Quality Index (AQI) . The AQI is based on the concentration levels of six major atmospheric pollutants: sulphur dioxide (SO), nitrogen dioxide (NO), suspended particulates smaller than 10 microns in diameter (PM10), carbon monoxide (CO), ozone (O), and suspended particulates smaller than 2.5 microns in diameter (PM2.5). The index is employed at monitoring stations in 367 cities across the nation.

The agency measures and assigns an individual air quality score (IAQI) to each of the six pollutants over a period of one, eight, or 24 hours. A city’s finial AQI is the highest of those six scores with that particular pollutant being the city’s major pollutant. When the index is lower than 50, the ministry does not name the major pollutant.