Dazu city in Chongqing is shrouded in morning fog. Why is Chongqing always full of smog?

Because of the terrain, most parts of Chongqing belong to the bottom of the valley, close to the Yangtze River, which leads to humid air in Chongqing, and water vapor is not easy to drift away, and fog is formed over time. On February 1 day, Dazu City in Chongqing was shrouded in morning fog, with tall buildings looming. The morning mist is spread in the air like a piece of white gauze and slowly swings in the breeze. People who live in tall buildings can see the wonders of fog and mist when they open their windows, just like a mirage.

One: The difference between fog and haze Fog is a natural phenomenon, and it is a visual phenomenon that small water droplets gather together in the atmosphere. Therefore, an important feature of fog is that the water vapor content reaches or approaches saturation, and the air contains water droplets or ice crystals.

Haze is a weather phenomenon caused by the accumulation of suspended particles in the air. These suspended particles are called smog particles. What is the technical term? Aerosol? . Haze is defined in meteorology as inorganic compounds, organic hydrocarbons and other particulate matter in the air, which can make the atmosphere turbid, blur the vision and lead to poor visibility. If the horizontal visibility is less than 10 km, the sight distance obstacle caused by this non-aqueous aerosol system is called haze. There are many components of haze particles. In China, the main components of smog particles are organic matter, sulfate, nitrate, ammonium salt, black carbon and so on. Smog particles have a great influence on horizontal visibility, usually smaller than 2.5 microns, which is called PM2.5

Two: How to distinguish fog from haze? Meteorology distinguishes fog and haze according to relative humidity and visibility. Fog appears when the relative humidity is higher than 95% and the visibility is lower than 10 km; When the relative humidity is lower than 80% and the visibility is lower than 10 km, it is haze; When the relative humidity is between 80% and 95% and the visibility is lower than 10 km, fog or haze appears. Pure fog is bluish white and milky white, as white as a fairyland. Haze pollution is often yellow and orange-gray, which is as gray as sandstorm. But now fog is not pure water droplets. Except for the less polluted areas, the fog in most areas is also dirty fog, and the pollutants contained in the fog droplets are also harmful to human health.

Empirically, fog and haze can be distinguished from each other in two aspects. The first is the duration. Fog comes quickly and dissipates quickly, usually from midnight to early morning, and it dissipates at sunrise. The appearance of smog is related to local pollution accumulation and regional pollutant transportation, which can last for a whole day or even weeks, and the smog pollution is more serious at night. The second is the boundary distribution. The boundary of fog is very clear, and it is unevenly distributed in the air. The closer to the ground, the greater the density. Although the haze pollution in the near-surface layer is more serious, the distribution of haze in the air is more uniform than that of fog. Fog and haze extend from the ground to the air at different heights. Usually, the thickness of fog is about several hundred meters, and the height of haze can reach 1~2 kilometers.