What are the characteristics of smog?

Particles such as dust, sulfuric acid, nitric acid and organic hydrocarbons in the air can also make the atmosphere turbid, blur the vision and worsen the visibility. If the horizontal visibility is less than 10000 meters, the visual distance obstacle caused by this non-aqueous aerosol system is called haze or dust haze, and the Hong Kong Observatory calls it haze.

Haze is an aggregate of a large number of tiny dust particles, smoke particles or salt particles suspended in the atmosphere, which makes the air turbid and reduces the horizontal visibility to below 10km. Haze is generally milky white, which weakens the color of objects, making bright objects in the distance appear red and yellow, while dark objects appear red and blue. The particles that make up the haze are too small to be distinguished by the naked eye. Due to various reasons, atmospheric condensation nuclei will also form haze when they grow up. In this case, the further condensation of water vapor may make haze evolve into light fog, fog and cloud. Haze is mainly composed of aerosols, which may appear at any time of the day.

Haze is also called atmospheric brown cloud. In the ground meteorological observation standard of China Meteorological Bureau, the definition of haze weather is: "A large number of extremely fine dry dust particles float evenly in the air, making the air with horizontal visibility less than 10 km generally cloudy, making bright objects in the distance slightly yellow and red, and making darker objects slightly blue." There are four areas with severe smog in some parts of China: Huanghuaihai area, Yangtze River basin, Sichuan basin and Pearl River Delta.