Study difference between fog and haze based on laser ceilometer

Based on CL51 laser ceilometer data at Daxing Station from October 2016 to February 2017, we analyze the intensity distribution of backscattering at six levels including fog, haze, slight haze, mist, and clear sky, compared the distribution probability of the vertical rate of change of the backscattering intensity of haze and fog. We also compared distribution probability of the average absolute value of the backscattering intensity gradient profile of slight haze and mist. The result shows: the backscattering intensity in the fog layer decreases significantly with the increase in height. In foggy weather, the distribution probability of backscattering intensity is close to clear sky above 300m, the thickness of fog generally does not exceed 300m. Since the particles of the haze layer are evenly distributed, the backscattering intensity in the haze layer changes more slowly with height than in the fog layer, and the thickness of the haze layer is generally greater than 500m. In foggy weather, the absolute value of the vertical rate of change of the backscattering intensity at a height of 0~300m is larger, it is smaller at a height higher than 300m. Since the particles distribution of the haze layer is more uniform than that of the fog layer, in most cases the absolute value of the vertical change rate of the foggy weather near the ground layer (0-100m) is greater than that of the haze weather. There is no obvious difference between the distribution probability of the vertical change rate of the backscattering intensity near the ground layer of slight haze and that of mist. However, in most cases, the absolute average value of the vertical gradient near the ground of mist is significantly greater than that of slight haze.