When the air quality reaches the excellent standard, it means that the air pollution index is less than or equal to 100. If the air pollution index is less than or equal to 50, the air quality is excellent. When the air pollution index is greater than 50 and less than or equal to 100, the air quality is good.
Air pollution index is to determine the classification of pollution index and the corresponding pollutant concentration value according to the ambient air quality standard and the influence of various pollutants on human health and ecological environment. The air pollution index (API) currently used in China is divided into five grades.
1, and the API value is less than or equal to 50, indicating that the air quality is excellent, which is equivalent to the national first-class air quality standard and meets the air quality requirements of areas requiring special protection such as nature reserves and scenic spots.
2. The 2.API value is greater than 50 and less than or equal to 100, indicating that the air quality is good, which is equivalent to reaching the national secondary quality standard.
3. The 3.API value is greater than 100 and less than or equal to 200, indicating that the air quality is slightly polluted, which is equivalent to the national air quality third-class standard.
4.API value greater than 200 indicates that the air quality is poor, which is called moderate pollution and is the national air quality level 4 standard.
5.API greater than 300 indicates that the air quality is extremely poor and has been seriously polluted.
Physical characteristics of air:
Density: Under standard conditions, the air density is 1.293kg/m3.
Pressure: Air pressure is the pressure caused by static gravity caused by the gravity of the earth above a place. Air pressure is affected not only by the measured height, but also by temperature and aerodynamic force. The air pressure on one square meter of sea level is about 10336 kg.
Temperature: Air temperature refers to the temperature of the air near the ground without being heated by solar radiation or ground heat sources. Different applications have different definitions of temperature. In meteorology, temperature is defined as the temperature two meters above the ground.
Humidity: Humidity is the composition of water vapor in the air.
Others: the sound speed of air in standard state is 331.5m/s. The molar mass of dry air was 28.9634 g/mol. In the standard state, the refractive index of air to visible light is about 1.00029. It varies with air pressure, temperature and air composition. In particular, humidity has a great influence on the refractive index, and the corresponding speed of light will also change in the air.