Explain from a geographical point of view. Why is there fog in Beijing? Pay attention to geographical reasons, such as atmospheric conditions, economic reasons or natural reasons.

1. From the atmospheric point of view, although Beijing has a monsoon climate, its internal circulation is obvious. 2. Geographically, Yanshan Mountain in the north of Beijing and Taihang Mountain in the southwest have some obstacles to the spread of pollution. However, the existence of northwest tuyere is also beneficial to the diffusion of pollutants, which is more beneficial than that of central and southern Hebei. The loess plateau in the west of Beijing has loose soil and is in the downwind direction of winter wind, with more dust. 3. Economically, Beijing is the second largest economic city in China, with less vegetation coverage and weak ability to repair pollution; There are many cars, and the air pollution is serious. There are many motor vehicles, which bring dust and tail gas. Industrial waste gas pollution, the mixture of steam and flue gas brought by boiler desulfurization facilities in winter pollutes the environment.

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