API calculation

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A network of air monitoring stations has been established in Hong Kong (the stations are shown in Figure 1.3) and real-time air quality data taken from each monitoring station are transmitted via telephone lines to the air quality data processing centre in the EPD office for the calculation of API.

Figure 1.3 The Hong Kong air quality monitoring network

 

Table 1.7 API sub-index levels & their corresponding concentrations

API sub-index level	Relationship with HKAQO	Corresponding concentrations (µg/m3)
		RSP 24-hr	SO2 24-hr	SO2 1-hr	NO2 24-hr	NO2 1-hr	CO 8-hr	CO 1-hr	O3 1-hr
0	-	0	0	0	0	0	0	0	0
25	50% Annual HKAQO / 25% HKAQO	28	40	200	40	75	2500	7500	60
50	Annual HKAQO / 50% HKAQO	55	80	400	80	150	5000	15000	120
100	HKAQO	180	350	800	150	300	10000	30000	240
200	-	350	800	1600	280	1130	17000	60000	400
300	-	420	1600	2400	565	2260	34000	90000	800
400	-	500	2100	3200	750	3000	46000	120000	1000
500	-	600	2620	4000	940	3750	57000	150000	1200

 

To view readings of the API for the last 24 hours, click here.