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Air Quality Index AQI

The Chinese name of the AQI we often say is called the Air Pollution Index (Air Quality Index, abbreviated AQI), which is based on the environmental air quality standards and the impact of various pollutants on human health, ecology, and the environment. Concentration is simplified into a single conceptual index value form, which classifies the degree of air pollution and air quality, and is suitable for expressing the short-term air quality status and trend of the city. For individual pollutants, air quality sub-indexes are also provided. The main pollutants involved in air quality evaluation are fine particulate matter, inhalable particulate matter, sulfur dioxide, nitrogen dioxide, ozone, and carbon monoxide.

Many people, including some experts, sometimes misunderstand AQI:

  • Aqi is not pm2.5?
  • pm2.5 has more than 200, why is aqi only 100?
  • Nobody can be seen outside, why do you still say that the air quality is good?

I hope that after reading this article, you can learn more about the air quality index that is closely related to us.

Air Quality Standard

In the first half of 2012, regulations were issued to replace the original air pollution index (API) with the air quality index (AQI).

Air quality is divided into six levels according to the size of the air quality index, corresponding to the six categories of air quality. The larger the index and the higher the level, the more serious the pollution and the greater the harm to human health. The first level is superior. Grade two is good, grade three is light pollution, grade four is moderate pollution, to grade five severe pollution, and grade six is ​​severe pollution. When the average daily concentration of PM2.5 reaches 150 μg/m3, the AQI reaches 200; when the average daily concentration of PM2.5 reaches 250 μg/m3, the AQI reaches 300; the average daily concentration of PM2.5 reaches 500 μg/ For cubic meters, the corresponding AQI index reaches 500.

According to the “Ambient Air Quality Index (AQI) Technical Regulations (Trial)” (HJ 633-2012), the air pollution index is divided into 0-50, 51-100, 101-150, 151-200, 201-300 and greater than 300 The sixth gear corresponds to the six levels of air quality. The larger the index, the higher the level, the more serious the pollution and the more obvious the impact on human health.

  • The air pollution index is 0-50, the air quality level is level 1, and the air quality status is excellent. At this time, the air quality is satisfactory, there is basically no air pollution, and all kinds of people can move normally.
  • The air pollution index is 51-100, the air quality level is second, and the air quality is in good condition. At this time, the air quality is acceptable, but certain pollutants may have a weak impact on the health of a very small number of extremely sensitive people. It is recommended that a very small number of extremely sensitive people should reduce outdoor activities.
  • The air pollution index is 101-150, the air quality level is three, and the air quality status is lightly polluted. At this time, the symptoms of susceptible people are slightly aggravated, and healthy people have irritation symptoms. It is recommended that children, the elderly, and patients with heart and respiratory diseases should reduce long-term, high-intensity outdoor exercise.
  • The air pollution index is 151-200, the air quality level is four, and the air quality status is moderately polluted. At this time, further aggravating the symptoms of susceptible people may affect the heart and respiratory system of healthy people. It is recommended that disease patients avoid long-term, high-intensity outdoor exercise, and the general population should reduce outdoor exercise appropriately.
  • The air pollution index is 201-300, the air quality level is five, and the air quality status is heavy pollution. At this time, patients with heart disease and lung disease have significantly worsened symptoms, reduced exercise tolerance, and symptoms generally appear in healthy people. It is recommended that children, the elderly, and patients with heart and lung diseases should stay indoors and stop outdoor exercise, and the general population should reduce outdoor exercise.
  • The air pollution index is greater than 300, the air quality level is six, and the air quality status is serious pollution. At this time, healthy people have reduced exercise tolerance, have obvious strong symptoms, and some diseases appear early. It is recommended that children, the elderly and patients should stay indoors to avoid physical exertion, and the general population should avoid outdoor activities.

Calculation method

The first step is to compare the graded concentration limits of various pollutants (refer to the concentration limit of AQI (GB3095-2012), and refer to the concentration limit of API (GB3095-1996)), and use fine particulate matter (PM2.5), The measured concentration values ​​of inhaled particulate matter (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO) and other pollutants (PM2.5 and PM10 are the 24-hour average concentrations) respectively Calculate the Air Quality Index (Individual Air Quality Index, IAQI); AQI calculation method 1

Where:

  • IAQIP-air quality sub-index of pollutant item P;
  • CP——The mass concentration value of pollutant item P;
  • BPHi——The air quality sub-index of the corresponding area and the high value of the pollutant concentration limit close to CP in the corresponding pollutant item concentration index table;
  • BPLo——The low value of the air quality sub-index of the corresponding area and the pollutant concentration limit close to the CP in the corresponding pollutant item concentration index table;
  • IAQIHi-the air quality sub-index of the corresponding area and the corresponding air quality sub-index of BPHi in the corresponding pollutant item concentration index table;
  • IAQILo-the air quality sub-index of the corresponding area and the corresponding air quality sub-index of BPLo in the corresponding pollutant item concentration index table.

The second step is to select the maximum value from the IAQI of various pollutants to determine the AQI. When the AQI is greater than 50, the pollutant with the largest IAQI is determined as the primary pollutant; AQI calculation method 1

Where:

  • IAQI-Air Quality Index;
  • n-pollutant item.

The third step is to compare the AQI grading standards to determine the air quality level, category and color, health effects and recommended measures. In short, AQI is the maximum value of the Air Quality Index (IAQI) of various pollutants. When the AQI is greater than 50, the corresponding pollutant is the primary pollutant. Pollutants with IAQI greater than 100 are excessive pollutants.

China-US air quality differences

China-US AQI standards and technical regulations: China’s air quality standards come from the “Ambient Air Quality Standards” (GB3095-2012) and “Ambient Air Quality Index (AQI) Technical Regulations (Trial)” (HJ633-2012) issued by the Ministry of Environmental Protection. (Hereinafter referred to as the “Regulations”); American standards come from a series of standards and technical specifications published on the official website of the U.S. Environmental Protection Agency (EPA) (http://www.epa.gov/), including technical help documents for daily air quality reports— ——Air Quality Index (AQI), Ambient Air Quality Standard (NAAQS), Air Volume Index (AQI), etc.

  1. The AQI calculation formulas are the same between China and the United States. The AQI standard classification, pollutant items, average time and concentration limits are formulated according to their respective ambient air quality standards; in the calculation of PM2.5 and PM10 air quality sub-indexes, the United States uses NowCast calculations Method, the algorithm can quickly respond to changing air quality conditions; China uses the 24-hour average of particulate matter instead of the 1-hour average to calculate the air quality sub-index of PM2.5 and PM10, which will increase the pollution level.

  2. China’s particulate matter concentration limit has certain problems, mainly manifested in the relatively loose evaluation standard of China’s PM2.524h average concentration limit when AQI<200, which leads to the phenomenon that the ratio of PM2.5/PM10 does not match the actual situation; In the case of good air quality, that is, when AQI=50, the ratio of PM2.5/PM10 is 0.7, which does not match the actual situation.

  3. The data analysis results of the monitoring points of Beijing Olympic Sports Center show that when AQI<50, the ratio of PM2.5/PM10 is less than 0.5, and the ratio of PM2.5/PM10 increases with the increase of the pollution index. It is recommended that China revise and adjust the concentration limits for real-time particulate matter reporting as soon as possible and improve its calculation methods.