Why is there moderate pollution in Zixing city?

Zixing city will have moderate pollution. The condition of moderate pollution in the weather is that the whole pressure field is very uniform, no large high and low pressure centers are formed, and the temperature rises. The temperature is between 5-8 degrees above zero and 3-5 degrees below zero, the relative humidity reaches 85-95%, and the breeze does not exceed 3 meters per second. The visibility is less than 50 meters, and the weather phenomenon is smog, which will reach moderate pollution.