The API system in China Air quality Before June 2000 Class API S02 NOx TSP I 0-50 0.000-0.050 0.000-0.050 0.000-0.120 Ⅱ 50-100 0.050-0.150 0.050-0.100 0.120-0.300 Ⅲ 100-200 0.150-0.250 0.100-0.150 0.300-0.500 V 200-300 0.250-1.600 0.150-0.565 0.500-0.625 V 300-400 1.600-2.100 0.565-0.750 0.625-0.875 400-500 2.100-2.620 0.750-0.940 0.875-1.000 Air quality After June 2000 Class API S02 NO2 PMio I 0-50 0.000-0.050 0.000-0.080 0.000-0.050 Ⅱ 50-100 0.050-0.150 0.080-0.120 0.050-0.150 Ⅲ 100-200 0.150-0.800 0.120-0.280 0.150-0.350 N 200-300 0.800-1.600 0.280-0.565 0.350-0.425 V 300-400 1.600-2.100 0.565-0.750 0.420-0.500 400-500 2.100-2.620 0.750-0.940 0.500-0.600The API system in China Air quality Class API Before June 2000 SO2 NOX TSP Ⅰ 0-50 0.000-0.050 0.000-0.050 0.000-0.120 Ⅱ 50-100 0.050-0.150 0.050-0.100 0.120-0.300 Ⅲ 100-200 0.150-0.250 0.100-0.150 0.300-0.500 Ⅳ 200-300 0.250-1.600 0.150-0.565 0.500-0.625 Ⅴ 300-400 1.600-2.100 0.565-0.750 0.625-0.875 400-500 2.100-2.620 0.750-0.940 0.875-1.000 Air quality After June 2000 Class API SO2 NO2 PM10 Ⅰ 0-50 0.000-0.050 0.000-0.080 0.000-0.050 Ⅱ 50-100 0.050-0.150 0.080-0.120 0.050-0.150 Ⅲ 100-200 0.150-0.800 0.120-0.280 0.150-0.350 Ⅳ 200-300 0.800-1.600 0.280-0.565 0.350-0.425 Ⅴ 300-400 1.600-2.100 0.565-0.750 0.420-0.500 400-500 2.100-2.620 0.750-0.940 0.500-0.600