Why is it easy to have smog in winter and not in summer?

It is not that there is no smog in spring, summer and autumn, but the formation of relatively little smog is a very complicated process, which is related to many aspects. The first is the climatic conditions. Generally, smog mostly occurs in autumn and winter. Due to the domestic climatic conditions, there are few air currents in autumn and winter, mostly pure and stable air currents, and less rain, which is suitable for pollutant accumulation. Then there are pollutants. There are many air pollution sources that cause smog, such as automobile exhaust, industrial waste gas, coal-fired power, petroleum products and so on. Thirdly, the pollutants in front of us, such as the pollution caused by heating coal in winter in the north, are also great sources of pollution. There is also the destruction of vegetation environment, which makes nature's ability to degrade smog decline rapidly and smog increases!