What is the definition of haze weather?

Haze is a general term for fog and haze. There is a great difference between fog and haze. Haze refers to the visual impairment caused by the aerosol system composed of dust, sulfuric acid, nitric acid and other non-aqueous substances in the smog air. When water vapor condensation intensifies and air humidity increases, haze will turn into fog. The difference between haze and fog is that the relative humidity is not large when haze occurs, but the relative humidity in fog is saturated.

Haze weather is a state of air pollution, and smog is a general term for the excessive content of various suspended particles in the atmosphere, especially PM2.5 (particles with a particle size less than 2.5 microns) is considered to be the "culprit" causing haze weather. There are many sources of smog, such as automobile exhaust, industrial emissions, building dust, garbage incineration, and even volcanic eruption. Hazy weather is usually formed by the mixed action of various pollution sources. However, in smog weather in different regions, different pollution sources have different functions.

Generally speaking, visibility less than 10 km is a haze phenomenon, less than 5 ~ 8 km is a moderate haze phenomenon, less than 3 ~ 5 km is a severe haze phenomenon, and less than 3 km is a serious haze phenomenon.