Why is the weather in Shijiazhuang always gray?

The poor air quality in cities is related to geographical location and, more importantly, human factors. Shijiazhuang was originally low-lying and surrounded by mountains, which had an urban heat island effect. The weather changes greatly, sometimes hot and sometimes cold.

According to this situation: the air is not circulating, the quality is not good, and it is depressed. It can be said that this is harmful to health.