What's the difference between cloudy and foggy days?

Generally speaking, the difference between fog and haze mainly lies in the water content: fog with water content above 90% in the morning and haze with water content below 80%. Between 80% and 90%, it is a mixture of fog and haze, but the main component is haze. In terms of visibility, if the horizontal visibility of the target is reduced to less than 1 km, it is fog; The horizontal visibility is between 1 km and1km, which is called light fog or haze; The horizontal visibility is less than 10 km, which is caused by dust particles, that is, haze or ash haze. In addition, there are some visible "differences" between haze and fog: the thickness of fog is only tens of meters to 200 meters, while haze is 1 km to 3 kilometers; The colors of fog are milky white and bluish white, while haze is yellow and orange gray. The boundary of fog is clear, and it may be clear in Wan Li after passing through the "fog area", but the boundary between haze and surrounding environment is not obvious.