Abstract: To reveal the transformation mechanism of fog and haze process, the level of air circulation, meteorological elements, concentrations of air contaminants and characteristics of atmospheric boundary layer of a persistent fog and haze process in Jinzhou city of Liaoning province from December 17 to 22, 2016, were analyzed using the conventional meteorological observation data, pollution monitoring data and the sounding data. The results indicate that zonal circulation situation and the steady boundary layer are favorable for haze to occur in terms of circulation features. The change of relative humidity is the transformation condition of fog-haze weather. When the air is not saturated, with the growth of humidity, pollutants increases, and the haze process intensifies; when the air is saturated, pollutant particles are activated to form fog droplets, completing the process of haze transformation into fog. A strong inversion layer and the stable atmosphere keep the haze. Thickness of mixed layer is a negative correlation with pollutant concentrations, the thinner the thickness of mixed layer is, the higher the pollutant concentrations are, and the visibility will be worse. At the same time, the change of the visibility and pollutant concentrations lagged behind the thickness of the mixed layer, and the thickness of the mixed layer of haze was larger than the fog was generated. By analyzing the tumble effect in the V-3θ diagram, anti-clockwise turns into clockwise when fog turns into haze.

Key words: fog and haze, the thickness of mixed layer, V-3θ diagram, Nozaki method, national standard method, Jinzhou city