The concept of haze weather?

Fog is an aerosol system composed of a large number of tiny water droplets or ice crystals suspended in the air near the ground, and it is the product of condensation (or sublimation) of water vapor in the air near the ground. The existence of fog will reduce air transparency and worsen visibility. If the horizontal visibility of the target drops below 1000 meters, the weather phenomenon of water vapor condensation (or condensation) suspended in the air near the ground is called fog. The phenomenon that the horizontal visibility of the target is 1000- 10000 meters is called light fog or mist. When fog is formed, the atmospheric humidity should be saturated (if there are a large number of condensation nuclei, the relative humidity may not reach 100%, and saturation may occur).

As far as its physical essence is concerned, fog and cloud are the products of condensation (or condensation) of water vapor in the air, so fog becomes a cloud when it rises from the ground, and it is called fog when it falls to the ground or moves to the mountains. Generally, the thickness of fog is relatively small, and the thickness of common radiation fog is between tens of meters and one hundred and two hundred meters. Fog, like clouds, has obvious boundary with clear sky area, and the droplet concentration distribution is uneven. The droplet size is large, ranging from a few microns to 100 micron, with an average diameter of about 10-20 micron. The naked eye can see the droplets floating in the air. Because the light scattered by fog composed of liquid water or ice crystals has little to do with wavelength, the fog looks milky white or bluish white.

Haze is also called haze (mái). Particulate matter such as dust, sulfuric acid, nitric acid and organic hydrocarbons in the air make the atmosphere turbid, blur the vision and make the visibility worse. If the horizontal visibility is less than 65,438+00,000 meters, the sight distance obstacle caused by this non-aqueous aerosol system is called haze or dust haze, and the Hong Kong Observatory calls it 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.

With the deterioration of air quality, cloudy days are increasing and the harm is increasing. Recently, many areas in China have incorporated the smog weather phenomenon into the fog as an early warning and forecast of disastrous weather. Collectively referred to as "haze weather".

The causes of smog in this section started from 20 13 65438+ 10/0, and Beijing, Tianjin, Hebei, Henan, Jiangsu and other places were shrouded in smog, with low visibility and high pollution. The Central Meteorological Observatory 13 continued to issue yellow fog warning. It is estimated that there will be fog with visibility less than 1000m in the above areas on 13, and visibility less than 200m in some areas.

Ma Xuekuan, chief forecaster of the Central Meteorological Observatory, said that when the suspended water vapor in the atmosphere condenses and the visibility is lower than 1000 meters, it is called fog in meteorology.

He said that when the water vapor contained in the air reaches the maximum, it will be saturated. If the water vapor exceeds saturation, the excess will condense out and combine with tiny dust particles in the air to form small water droplets or ice crystals, which will be suspended in the air layer near the ground and become fog. The lower the temperature, the less water vapor can be contained in the air, and the easier it is to form smog.

In view of the specific meteorological conditions in Beijing, North China and other places, under the influence of low temperature, when the warm and humid southerly wind near the ground moves horizontally, it gradually cools down after passing through the cold ground or water surface to form fog.

Non-diffusion of pollutants Ma Xuekuan said: "Fog itself is not pollution, but the atmospheric environment that produces fog is in a relatively stable state. Pollutants in the air are not easy to spread outward, resulting in agglomeration effect, which will make pollution more and more serious. Similarly, under the conditions of low air pressure and low wind power, the combination of urban pollutants and water vapor in the lower air will also aggravate the degree of smog. "

Meteorologists said that because the fog itself presents an uneven phenomenon. Therefore, there will be different degrees of smog in the same city.

"Taking Beijing as an example, the fog in the south flows to the urban area, which leads to a decline in urban visibility. Due to the high terrain in the north, the probability of smog is smaller than that in the urban area. " Sun, chief forecaster of Beijing Meteorological Observatory, said.

The Central Meteorological Observatory predicts that the cold air activity in China will be weak in the next three to five days, and the central and eastern regions will still be in a foggy period.

"But the foggy weather in these areas is intermittent. 14- 15, there will be a cold air activity in the north, and the haze weather in some areas will also be weakened. Throughout the middle of 1 month, there were relatively many foggy days in the central and eastern regions, among which the high-incidence areas were North China Plain, Huanghuai Area and Sichuan Basin. " Ma Xuekuan said.

PM2.5 is the "culprit" in foggy days. There are many main sources. One is road dust and construction dust. According to research, road dust is the main source of PM2.5, accounting for about 40% of the source of PM2.5, followed by automobile exhaust. In recent years, there are more and more cars in cities, and the emission of automobile exhaust is also increasing, which makes a greater contribution to PM2.5 in urban air. The third is the secondary pollution produced by the factory. Fourth, the pollutants emitted by low-altitude coal burning during heating in winter. Fifth, the flue gas generated by the burning of biomass (straw and firewood) and garbage incineration is also an important source of PM2.5