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Air Quality Index

The definition of air pollution indicators

Air quality index based on monitoring data will be on the same day in the air ozone(O3), fine particulate matter(PM2.5), particulate matter(PM10), carbon monoxide(CO), sulfur dioxide(SO2) and II Nitric oxide(NO2) such as the concentration of value, its impact on human health, were converted into different pollutants The vice-value targets, indicators, deputy to the day of the maximum value of the stations on the day of the air quality index (AQI).

Introduction to air pollutants

  • PM2.5
  • PM10
  • SO2
  • NOX
  • CO
  • O3
  • ● PM2.5

    Construction site, transboundary, industry, open burning or Traffic caused pollution(surface aeolian dust or motor vehicle pollution)

  • ● PM10

    Construction site, transboundary, industry, open burning or Traffic caused pollution(surface aeolian dust or motor vehicle pollution)

  • ● SO2

    Volcanic gas or sulfufric burning in fossil fuel

  • ● NOX

    Nitrogen Oxide is formed during the process of nitride combustion. Nitride is the product of nitrogen oxide photochemical reaction.

  • ● CO

    Forest fire, methane nitridation, biological activity or incomplete combustion of fuel.

  • ● O3

    Secondary pollutants from nitrogen oxide, reactive hydrocarbons, or photochemical reaction.。

Introduction to air pollutants

Daily air quality indicator (Daily AQI)

Concentrations of ozone (O3), fine particulate matter (PM2.5), particulate matter (PM10), carbon monoxide (CO), sulfur dioxide (SO2) and nitrogen dioxide (NO2) in a day are converted into their corresponding sub-indicators based on their impacts on human health. The largest value of the sub-indicators is the AQI of the monitoring station on the day.

Air Quality Index (AQI)
AQI
Good0～50
Moderate51～100
Unhealthy for Sensitive Groups101～150
Unhealthy151～200
Very Unhealthy201～300
Hazardous301～400
Hazardous401～500
AQI O3 (ppm)
8h		 O3 (ppm)
1-h(1)		 PM2.5 (μg/m3 )
24-h		 PM10 (μg/m3 )
24-h		 CO (ppm)
8-h		 SO2 (ppb)
1-h		 NO2 (ppb)
1-h
Good0～50
 0.000 - 0.054 - 0.0 - 15.4 0-50 0 - 4.4 0-20 0-30
Moderate51～100
 0.055 - 0.070 - 15.5 - 35.4 51-100 4.5 - 9.4 21-75 31-100
Unhealthy for Sensitive Groups101～150
 0.071 - 0.085 0.125 - 0.164 35.5 - 54.4 101-254 9.5 - 12.4 76-185 101-360
Unhealthy151～200
 0.086 - 0.105 0.165 - 0.204 54.5 - 150.4 255-354 12.5 - 15.4 186-304(3) 361-649
Very Unhealthy201～300
 0.106 - 0.200 0.205 - 0.404 150.5 - 250.4 355-424 15.5 - 30.4 305-604(3) 650-1249
Hazardous301～400
 (2) 0.405 - 0.504 250.5 - 350.4 425 - 504 30.5 - 40.4 605-804(3) 1250-1649
Hazardous401～500
 (2) 0.505 - 0.604 350.5 - 500.4 505-604 40.5 - 50.4 805-1004(3) 1650-2049
  1. Areas are generally required to report the AQI based on 8-hour ozone values. However, there are a small number of areas where an AQI based on 1-hour ozone values would be more precautionary. In these cases, in addition to calculating the 8-hour ozone index value, the 1-hour ozone value may be calculated, and the maximum of the two values reported.
  2. 8-hour O3 values do not define higher AQI values (≥ 301). AQI values of 301 or higher are calculated with 1-hour O3 concentrations.
  3. 1-hour SO2 values do not define higher AQI values (≥ 200). AQI values of 200 or greater are calculated with 24-hour SO2 concentrations.

Real-time air quality indicator (real-time AQI)

The MOENV issues real-time AQI as a reference for issuing early warnings and provides hourly monitoring data. The calculation of real-time AQI is the following:

The real-time concentration of each item is calculated based on the following equations, and compared against the following table to obtain the real-time sub-indicators of O3, PM2.5, PM10, CO, SO2 and NO2. The largest sub-indicator is the real-time AQI, and its corresponding item is the leading pollutant.

  • ● O3, 8h： value of the last 8-hour moving average (e.g. the 8-hour average concentration value of O3 published at 10AM this morning is the average of monitoring data from 2AM to 9AM this morning)
  • ● O3： real-time concentration value
  • ● PM2.5：0.5 x average of the first 12 hours + 0.5 x average of the first 4 hours (2 entries of the first 4 hours are valid and 6 entries of the first 12 hours are valid)
  • ● PM10 ：0.5 x average of the first 12 hours + 0.5 x average of the first 4 hours (2 entries of the first 4 hours are valid and 6 entries of the first 12 hours are valid)
  • ● CO： value of the last 8-hour moving average (e.g. the 8-hour average concentration value of CO published at 10AM this morning is the average of monitoring data from 2AM to 9AM this morning)
  • ● SO2：real-time concentration value
  • ● SO2, 24h：average of concentration values in the last 24 hours (e.g. the 24-hour average concentration value of SO2 published at 10AM this morning is the average of monitoring data from 10AM yesterday to 9AM today)
  • ● NO2： real-time concentration value

Note：
a valid moving average of PM2.5 includes the first digit to the right of the decimal point, so the second digit to the right of the decimal point is rounded. Valid 8-hour moving average of O3 and moving average of PM10 should be integers, so the first digit to the right of the decimal point is rounded.

The concentration of pollutants and air quality index value deputy table
Pollutant
Statistical Methods
Unit
AQI
0～50
51～100
101～150
151～200
201～300
301～400
401～500
Pollutant O3 , 8h O3(1) PM2.5 PM10 CO SO2 NO2
Statistical Methods value of the last 8-hour moving average real-time concentration value 0.5 x average of the first 12 hours + 0.5 x average of the first 4 hours 0.5 x average of the first 12 hours + 0.5 x average of the first 4 hours value of the last 8-hour moving average real-time concentration value real-time concentration value
Unit ppm ppm μg/m3 μg/m3 ppm ppb ppb
AQI
0～50
 0.000 - 0.054 - 0.0 - 15.4 0-50 0-4.4 0-20 0-30
51～100
 0.055 - 0.070 - 15.5-35.4 51-100 4.5-9.4 21-75 31-100
101～150
 0.071 - 0.085 0.125 - 0.164 35.5-54.4 101-254 9.5-12.4 76-185 101-360
151～200
 0.086 - 0.105 0.165 - 0.204 54.5 - 150.4 255-354 12.5-15.4 186-304 (3) 361-649
201～300
 0.106 - 0.200 0.205 - 0.404 150.5 - 250.4 355 - 424 15.5-30.4 305-604(3) 650-1249
301～400
 (2) 0.405 - 0.504 250.5 - 350.4 425-504 30.5-40.4 605-804(3) 1250-1649
401～500
 (2) 0.505 - 0.604 350.5 - 500.4 505-604 40.5-50.4 805-1004(3) 1650-2049
  1. Areas are generally required to report the AQI based on 8-hour ozone values. However, there are a small number of areas where an AQI based on 1-hour ozone values would be more precautionary. In these cases, in addition to calculating the 8-hour ozone index value, the 1-hour ozone value may be calculated, and the maximum of the two values reported.
  2. 8-hour O3 values do not define higher AQI values (≥ 301). AQI values of 301 or higher are calculated with 1-hour O3 concentrations.
  3. 1-hour SO2 values do not define higher AQI values (≥ 200). AQI values of 200 or greater are calculated with 24-hour SO2 concentrations.

Go to home page for real-time consentration and AQI.

Air Quality Index and Activity Guidance

AQI
Air Quality Index Levels of Health Concern
Status Color
Impact on health
Activity Guidance for the General Public
Activity Guidance for Sensitive Groups
AQI 0-50 51-100 101-150 151-200 201-300 301-500
Air Quality Index Levels of Health Concern Good Moderate Unhealthy forSensitive Groups Unhealthy Very Unhealthy Hazardous
Status Color
Green
Yellow
Orange
Red
Purple
Maroon
Impact on Human Health Air quality is considered satisfactory, and air pollution poses little or no risk. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution. Members of sensitive groups may experience health effects. The general public is not likely to be affected. Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects. Health alert: everyone may experience more serious health effects. Health warnings of emergency conditions. The entire population is more likely to be affected.
Activity Guidance for the General Public Enjoy your usual outdoor activities. Enjoy your usual outdoor activities. 1..Everyone experiencing discomfort such as sore eyes, cough or sore throat should consider reducing outdoor activities.
2.For students, it’s ok to be active outside, but are recommended to reduce prolonged strenuous exercise.		 1.Everyone experiencing discomfort such as sore eyes, cough or sore throat should reduce physical exertion, particularly outdoors.
2.Students should avoid prolonged strenuous exercise, and take more breaks during outdoor activities.		 1.Everyone should reduce outdoor activities.
2.Students should stop outdoor activities and move all activities and classes indoors.		 1.Everyone should avoid outdoor activities and keep doors and windows closed. If it is necessary to go out, please wear a mask.
2.Students should stop outdoor activities and move all activities and classes indoors.
Activity Guidance for Sensitive Groups Enjoy your usual outdoor activities. Unusually sensitive groups are recommended to watch for symptoms such as coughing or shortness of breath, but can still be active outside. 1.People with heart, respiratory and cardiovascular problems, children, teenagers and older adults are recommended to reduce physical exertion and outdoor activities.
2.People with asthma may need to use their reliever inhalers more often.		 1.People with heart, respiratory and cardiovascular problems, children, teenagers and older adults are recommended to stay indoors and reduce physical exertion. If it is necessary to go out, please wear a mask.
2.People with asthma may need to use their reliever inhalers more often.		 1.People with heart, respiratory and cardiovascular problems, children, teenagers and older adults should stay indoors and reduce physical exertion. If it is necessary to go out, please wear a mask.
2.People with asthma should use their reliever inhalers more often.		 1.People with heart, respiratory and cardiovascular problems, children, teenagers and older adults should stay indoors and avoid physical exertion. If it is necessary to go out, please wear a mask.
2.People with asthma should use their reliever inhalers more often.