Table 1.

Threshold values of ambient air pollutant indicators in GB 3095-1996.

No.	Pollutant Indicator	Average Time	Threshold Values			Unit
			Level I	Level II	Level III
1	SO2	Annual mean	20	60	100	µg/m3
		24-hour average	50	150	250
		1-hour average	150	500	700
2	NO2	Annual mean	40	40	80	µg/m3
		24-hour average	80	80	120
		1-hour average	120	120	240
3	CO	24-hour average	4	4	6	mg/m3
		1-hour average	10	10	20
4	O3	1-hour average	120	160	200	µg/m3
5	PM10	Annual mean	40	100	150	µg/m3
		24-hour average	50	150	250