What does the smog in the weather forecast mean?

Also known as haze (called haze in Hong Kong), dust, sulfuric acid, nitric acid, organic hydrocarbons and other particulate matter in the air can also make the atmosphere turbid, blur the vision and worsen the visibility. If the horizontal visibility is less than 65,438+00,000 meters, the visual field obstacle caused by this non-aqueous aerosol system is called haze or dust haze. The difference between haze and fog is that the relative humidity is small when haze occurs, but it is saturated in fog (if there are a large number of condensation nuclei, the relative humidity may not reach 100%, and saturation may occur). Generally speaking, the visibility deterioration caused by atmospheric haze blurred vision is caused by haze when the relative humidity is less than 80%, while the visibility deterioration caused by atmospheric haze blurred vision is caused by fog when the relative humidity is more than 90%. The visibility deterioration caused by atmospheric haze blurred vision is caused by a mixture of haze and fog when the relative humidity is between 80 and 90%, but its main component is haze. The thickness of haze is relatively thick, which can reach about 1-3 km. Haze is different from fog and clouds, and there is no obvious boundary between haze and clear sky. Smog particles are evenly distributed, and the particle size is relatively small, ranging from 0.00 1 micron to 10 micron, with an average diameter of about 1-2 micron. Floating particles are invisible to the naked eye. Because the smog is composed of dust, sulfuric acid, nitric acid and other particles, the longer the scattering wavelength, the more the light ratio, so the smog looks yellow or orange-gray.

Formation of haze weather

Haze refers to the whole atmospheric turbidity phenomenon in the atmospheric boundary layer and even the lower troposphere, and the visibility is below 10 km. The atmospheric aerosols that form haze weather mainly come from natural emissions and human activities, but the total amount of aerosol particles emitted by natural emissions and human activities is basically stable for a period of time, so why sometimes severe haze weather occurs, and sometimes it is blue sky and white clouds? The decisive control factor is meteorological conditions. When haze weather appears, it is usually accompanied by still wind, strong sunshine and low relative humidity. Severe haze weather occurs under the condition of strong inversion of boundary layer without exception. The inversion layer is like a pot cover, which limits the diffusion and dilution of substances in it. On the other hand, the development of urbanization and industrialization has changed the attributes of the underlying surface and the physical structure of the urban atmospheric boundary layer. Generally speaking, the smog is caused by poor diffusion conditions in the city, weak cold air and weak wind speed. At this time, various pollutants in the city cannot spread in time and accumulate near the ground. If the weather is dry and rainy, the sunshine is strong, and the humidity is low, various photochemical reactions between pollutants are prone to form smog.

Automobile exhaust is an important factor in the formation of smog, so the smog situation will be particularly serious on the main roads with busy traffic, and the visibility is lower than other places.