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.   Category A B C D E F Description Good Moderate Unhealthy for sensitive groups Unhealthy Very unhealthy Hazardous 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   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     Good (0~50) Moderate (51~100) Unhealthy for sensitive groups (101~150) Unhealthy (151~250) Very unhealthy (251~350) Hazardous (351~500) Color Blue Green Yellow Orange Red Brown RGB Code 0000FF 00FF00 FFFF00 FF9900 FF0000 861313 Pictogram