The CAI is a way of describing ambient air quality based on health risk of air pollution. The index aims to help the public easily understand air quality level and protect the health of people from air pollution.
* Calculate the value of the CAI by pollutants
- The CAI has values of 0 through 500, which are divided into six categories. The higher the CAI value,    the greater the level of air pollution.
- Of values of the five air pollutants, the highest is the CAI value.
- Variables required in calculating the CAI
Category A B C D E F
Description Good Moderate Unhealthy for
sensitive groups
Unhealthy Very unhealthy Hazardous
Values ILO 0 51 101 151 251 351
IHI 50 100 150 250 350 500
Concentration BPLO BPHI BPLO BPHI BPLO BPHI BPLO BPHI BPLO BPHI BPLO BPHI
SO₂
(ppm)
1hr 0 0.020 0.021 0.050 0.051 0.100 0.101 0.150 0.151 0.400 0.401 1
NO₂
(ppm)
1hr 0 0.030 0.031 0.060 0.061 0.150 0.151 0.200 0.201 0.600 0.601 2
CO
(ppm)
1hr 0 2.00 2.01 9.00 9.01 12.00 12.01 15.00 15.01 30.00 30.01 50
O₃
(ppm)
1hr 0 0.040 0.041 0.080 0.081 0.120 0.121 0.300 0.301 0.500 0.501 0.600
PM-10
(㎍/㎥)
24hr 0 30 31 80 81 120 121 200 201 300 301 600
 
- PM-10 24hr(C24E): 24hr prediction moving average of PM-10
C24E = [C12 × 12 + C4 × 12]÷ 24
where,
C12 = Average of the past 12 hours
C4 = Average of the past 4 hours
     = ( Cai + Ca(i-1) + Ca(i-2) + Ca(i-3) ) ÷ 4
Ci = standard time measurement concentration (I = standard time)
Ci < 70 ⇒ Cai = Ci
Ci ≥70 , Ci/C12 < 0.9 or Ci/C12 > 1.7 ⇒ Cai = Ci
Ci ≥70 , 0.9 ≤ Ci/C12 ≤1.7 ⇒ Cai= 0.75 × Ci
 
- Understanding the CAI
Category Description Health Effects
A Good A level that will not impact patients suffering from diseases related to air pollution
B Moderate A level which may have a meager impact on patients in case of chronic exposure
C Unhealthy for sensitive groups A level that may have harmful impacts on patients and members of sensitive groups
D Unhealthy A level that may have harmful impacts on patients and members of sensitive groups (children, aged or weak people), and also cause the general public unpleasant feelings
E Very unhealthy A level which may have a serious impact on patients and members of sensitive groups in case of acute exposure
F Hazardous A level which may need to take emergency measures for patients and members of sensitive groups and have harmful impacts on the general public
 
※ If more than two pollutants are included in the categories of C,D,E, and F, additional values are    added to the CAI value;
- If one pollutant is included in one of those categories, its value becomes the CAI
- If two pollutants are included, the pollutant with the highest value is described as an responsible
  pollutant, and 50 values are added to the value of the responsible pollutant.
- If three pollutants are included, the pollutant with the highest value is described as an responsible
  pollutant, and 75 values are added to the value of the responsible pollutant.
 
 
where,
Ip = The air quality index for each target pollutant
Cp = The rounded concentration of each target pollutant
BPHI = The breakpoint that is greater than or equal to Cp
BPLO = The breakpoint that is less than or equal to Cp
IHI = The index value corresponding to BPHI
ILO = The index value corresponding to BPLO