The Air Quality Composite Index (AQI) is an important reference indicator for measuring air quality, which reflects the comprehensive status of air quality and gives a timely and accurate picture of outdoor air pollution levels. The following is a detailed explanation of the Air Quality Index (AQI):
Definition
AQI is a dimensionless index that describes the comprehensive condition of urban air quality and can be used to measure air quality over a long period of time, e.g., weekly, monthly and yearly. The larger its value, the heavier the combined pollution level is represented.
Evaluation Items
The evaluation items of AQI include:
Respirable particulate matter (PM10): particulate matter with an aerodynamic equivalent diameter of ≤10 microns in ambient air.
Fine particulate matter (PM2.5): particulate matter with an aerodynamic equivalent diameter of ≤2.5 microns in ambient air.
Ozone (O3): a gaseous pollutant.
Sulphur dioxide (SO2): a common gaseous pollutant.
Nitrogen dioxide (NO2): a common gaseous pollutant.
Carbon Monoxide (CO): a toxic gaseous pollutant.
Volatile organic compounds (VOCs): a class of organic compounds.
Calculation Method
The method of calculating the AQI involves two key steps:
Individual Quality Index Calculation: For each evaluation item, its individual quality index is calculated. The individual quality index is obtained by dividing the evaluated concentration value of the pollutant (Ci) by the standard value of the pollutant (Si). For example, if the standard limit value of PM10 is 70 μg/m³, and if the concentration of PM10 is 187 μg/m³, its individual mass index is 187/70 = 2.67.
Composite Index Calculation: Sum the individual quality indices of all evaluation items to get the composite air quality index. The larger the composite index, the heavier the degree of air pollution.
Air Quality Rating
According to the value of Air Quality Composite Index (AQI), air quality can be classified into six grades:
Grade I (Excellent): AQI between 0 and 50, air quality is satisfactory and basically free of air pollution.
Grade 2 (Good): AQI between 51 and 100, air quality is acceptable, but certain pollutants may have a weak impact on the health of a very small number of unusually sensitive people.
Level 3 (Slightly polluted): AQI between 101 and 150, with mild exacerbation of symptoms in susceptible groups and irritation in healthy groups.
Level 4 (Moderate Pollution): AQI between 151 and 200, further exacerbation of symptoms in susceptible populations, with possible effects on the heart and respiratory system in healthy populations.
Level 5 (Heavy Pollution): AQI between 201 and 300, with significant exacerbation of symptoms in people with heart and lung disease, reduced exercise tolerance, and generalised symptoms in healthy people.
Level 6 (Severe Pollution): AQI above 300, reduced exercise tolerance in the healthy population, markedly strong symptoms and early onset of certain diseases.
Above is a detailed explanation of the Air Quality Index (AQI), including definitions, evaluation items, calculation methods and air quality levels.