Table 1.

Calculation equation of Malaysia API sub-index for each pollutant based on Pollution Standard Index (PSI) (Source: Malaysian Department of Environment DOE).

Pollutant	API calculation equation
CO (Based on eight-hour average concentration)	conc. < 9 ppm	API = conc. X 11.11111
	9 < conc. < 15	API = 100 + {[conc. – 9] x 16.66667}
	15 < conc. < 30	API = 200 + {[conc. – 15] x 6.66667}
	conc. > 30 ppm	API = 300 + {[conc. -30] x 10}
O3 (Based on one-hour average concentration)	conc. < 0.2 ppm	API = conc. X 1000
	0.2 < conc. < 0.4	API = 200 + {[conc. – 0.2] x 500}
	conc. > 0.4 ppm	API = 300 + {[conc. – 0.4] x 1000}
NO2 (Based on one-hour average concentration)	conc. < 0.17 ppm	API = conc. X 588.23529
	0.17 < conc. < 0.6	API = 100 + {[conc. – 0.17] x 232.56}
	0.6 < conc. < 1.2	API = 200 + {[conc. – 0.6] x 166.667}
	conc. > 1.2 ppm	API = 300 + {[conc. – 1.2] x 250}
SO2 (Based on 24-hour average concentration)	conc. < 0.04 ppm	API = conc. X 2500
	0.04 < conc. < 0.3	API = 100 + {[conc. – 0.04] x 384.61}
	0.3 < conc. < 0.6	API = 200 + {[conc. – 0.3] x 333.333}
	conc. > 0.6 ppm	API = 300 + {[conc. – 0.6] x 500}
PM10 (Based on 24-hour average concentration)	conc. < 50 pg/m3	API = conc.
	50 < conc. < 150	API = 50 + {[conc. – 50] x 0.5}
	150 < conc. < 350	API = 100 + {[conc. – 150] x 0.5}
	350 < conc. < 420	API = 200 + {[conc. – 350] x 14286}
	420 < conc. <500	API = 300 + {[conc. – 420] x 1.25}
	conc. > 500 pg/m3	API = 400 + [conc. – 500]