Good	Fair	Moderate	Poor	Very poor
Particles less than 2.5 µm (PM2.5)	0-10	10-20	20-25	25-50	50-800
Particles less than 10 µm (PM10)	0-20	20-35	35-50	50-100	100-1200
Nitrogen dioxide (NO2)	0-40	40-100	100-200	200-400	400-1000
Ozone (O3)	0-80	80-120	120-180	180-240	240-600
Sulphur dioxide (SO2)	0-100	100-200	200-350	350-500	500-1250
Index level (based on pollutant concentrations in µg/m3)