What climate geography does ∞ stand for?

The sign of smog is "∞". The diurnal variation of haze is generally not obvious. When the air mass changes little and is stable, it lasts for a long time, sometimes exceeding 10 days. Due to the weather phenomena such as smoke, light fog, sandstorm, sand blowing, floating dust and haze, the effective horizontal visibility is less than 10KM due to the influence of a large number of extremely fine dust particles or smoke particles floating in the air. Sometimes it is difficult for meteorological professionals to tell the difference. It is necessary to comprehensively analyze and judge the weather background, sky conditions, air humidity, color and smell, satellite monitoring and other factors in order to draw a correct conclusion. The weather phenomena of fog and haze can sometimes be converted to each other.