The following table records the weather quality of several cities in China in April of a certain year, making the urban air quality reach Grade I and Grade II.

Shanghai 7/ 10*30=2 1

Shenyang 2/3*30=20

Taiyuan 1/2*30= 15

Dalian 14/ 15*30=28

Dalian has the most days to reach the standard.

The air quality reflects the degree of air pollution, which is judged according to the concentration of pollutants in the air. Air pollution is a complex phenomenon. At a specific time and place, the concentration of air pollutants is affected by many factors.

Noun explanation:

Fine particles, also known as fine particles, fine particles and PM2.5 fine particles, refer to particles with aerodynamic equivalent diameter less than or equal to 2.5 microns in ambient air. It can be suspended in the air for a long time, and the higher its concentration in the air, the more serious the air pollution. Although PM2.5 is only a small part of the composition of the earth's atmosphere, it has an important impact on air quality and visibility.

Compared with atmospheric coarse particles, PM2.5 has the advantages of small particle size, large area, strong activity and easy attachment of toxic and harmful substances (such as heavy metals and microorganisms). ), it stays in the atmosphere for a long time and has a long transportation distance, so it has a great impact on human health and atmospheric environmental quality.