Why is the smog more serious in winter? Many times, smog appears all over the country at the same time.

The smog in winter is mainly caused by inversion, and there are many reasons for the emission of heating pollutants in winter.

In winter, due to the obvious ground radiation cooling at night, the "inversion layer" is easy to appear in the low altitude of the atmosphere, and the exchange and circulation ability of air in the horizontal and vertical directions becomes weak. The pollutants discharged into the air are confined in the shallow atmosphere and gradually gather into smog, leading to air pollution. At the same time, foggy days appear more frequently in winter. This is because the winter nights are long, there are more opportunities for sunny days and small winds, the ground heat dissipation is faster, and the temperature drop is more significant. When the temperature drops to the lowest in the morning, the water vapor in the air is easy to reach saturation and condense into small water droplets, which accumulate more and more and form fog.

From the meteorological point of view, when there is fog, it often means that the atmosphere is relatively stable, and the stable atmosphere is easy to accumulate pollutants, so foggy days are usually accompanied by mild or severe pollution. In many cases, low visibility weather is actually caused by the mixture of fog and haze. When the relative humidity is high in the morning, it is mostly fog, and it turns into haze after the temperature rises and the humidity drops during the day. Especially under the influence of heating, more pollutants are discharged in winter, which is also an important cause of winter smog.

What is inversion?

In the lower atmosphere, the atmospheric temperature decreases with the increase of altitude, and the temperature decreases by about 0.6 degrees Celsius for every increase of 100 meter. That is to say, below a few kilometers, the lower atmosphere is generally high in temperature and low in density, while the upper atmosphere is low in temperature and high in density. This atmospheric structure is prone to up-and-down convection movement, which can transport and spread pollutants near the ground to high altitude and long distance, thus reducing the pollution degree above the ground. Under some weather conditions, the atmospheric structure above the ground will have an abnormal phenomenon that the temperature increases with the increase of height, which is called "inversion", and the atmosphere with inversion phenomenon is called "inversion layer". It is like a thick quilt covering the sky, which reduces the air flow between the upper and lower layers. The air pollutants near the ground have no way to go, so they have to stay where they are. The more they accumulate, the heavier the air pollution will be.