What kind of meteorological conditions are needed to form smog?

There is a negative correlation between wind and the number of haze, that is, the greater the wind speed, the less the number of haze weather.

Wind has two main effects on smog. The first is horizontal transportation. Suspended particles in the atmosphere will be transported in parallel to the surrounding cities and regions under the impetus of wind speed. Although the air quality in windy cities has improved, the pollutants have not decreased, but moved to another city.

The second is dilution. Air pollutants will move with the wind speed and mix with the surrounding clean air, resulting in the reduction of particles with the same volume, thus improving air quality.

Both methods can improve the air quality in cities. The greater the wind speed, the better the air quality. Therefore, when the wind is strong, there are few persistent severe polluted weather, which is also the reason why some cities build ventilation corridors to improve the air.

Second, what impact will precipitation have on smog?

Precipitation refers to the phenomenon that water vapor in the air condenses and falls to the surface. It includes two parts, one is horizontal precipitation, such as fog and frost, and the other is vertical precipitation, such as rain and snow. Either way, as long as the precipitation reaches a certain level, it will have a certain scouring effect on the smog particles in the air.

Everyone should have had this experience. If there is a heavy rain in the fog, after the rain stops, the weather turns blue, the visibility improves and the air becomes fresh. This is because the heavy rain has settled the smog particles in the air to the ground. However, if the rainfall is relatively small, especially the continuous rain in Mao Mao, the haze weather will not improve, but may worsen. At this time, because the rain in Mao Mao has increased the air humidity, but whether it exceeds 60%, it is particularly easy to form smog.

Third, the impact of urban heat island effect on smog?

Urban heat island effect refers to the phenomenon of "high temperature" in cities due to a large number of artificial heating, buildings and roads, and the reduction of green space. The temperature in general cities is significantly higher than that in peripheral suburbs. Haze and urban heat island effect will influence and promote each other.

When there is fog, all kinds of smog particles and smoke dust over the city will absorb a lot of long-wave thermal radiation. In addition, the dense buildings in the city block the passage of incoming air, reduce the wind speed, affect the diffusion of heat and increase the urban heat island effect. At the same time, after the urban heat island effect is enhanced, the near-surface temperature rises and the air moves upward, forming a low-pressure vortex, which will lead to the accumulation of atmospheric pollutants in the central area of the city and increase the possibility of smog.