How is the smog in Beijing formed?

Causes of smog in Beijing, official explanation information:

References:

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First, the special climate background and extreme meteorological conditions. 20 15 is the strongest year of El Ni? o since historical statistics, and extreme weather occurs frequently all over the world. Since June 1 1, North China has suffered from heavy snowfall. The melting of snowfall has caused the surface humidity to approach saturation and the temperature to drop, while the middle atmosphere has obviously warmed up, resulting in extremely unfavorable meteorological conditions of high humidity, low wind speed and strong inversion temperature in a large area of North China, and pollution continues to accumulate.

The second is the emission of pollution sources such as coal burning and motor vehicles in the region. Coal burning and motor vehicles are still the main sources of pollution. After entering the heating period, coal-fired pollution emissions increased significantly, especially in the process of snowfall and cooling in the early stage, which led to a significant increase in regional coal-fired heating consumption. At the same time, under the static and low visibility weather conditions, road congestion is aggravated, fuel efficiency is reduced, and vehicle pollution emissions are also significantly increased. In addition, continuous high humidity and static meteorological conditions are conducive to the transformation of gaseous pollutants into particulate matter, as well as the moisture absorption growth of particulate matter, which makes the concentration level of PM2.5 rise.