When is the smog the most serious?

Under normal circumstances, smog mostly occurs in autumn and winter, especially in cold winter, and the highest is more serious. However, meteorologists say that the occurrence of haze days is not limited by seasons. Although it is more frequent in autumn and winter, it will still appear in spring and summer. Haze weather has obvious seasonality, mainly in autumn and winter, because of low temperature and weak ground pressure field. The wind force near the ground is small, if there is no cold air activity, the atmospheric stratification will be relatively stable, and there is an inversion layer near the ground, which is not conducive to the dilution and diffusion of pollutants. At this time, if the humidity is high, it is easy to form haze weather.