Abstract:Using conventional meteorological observation data, sounding data, pollutant concentration and AQI data, NCEP reanalysis data, the causes of a severe persistent fog-haze weather in Changzhou from November 24 to December 3, 2018 were analyzed. The results show that this fog-haze process lasted a long time with wide scope, large density and heavy pollution. The upper latitudinal circulation was dominant in the upper latitudes during the fog-haze period, and the warm ridges in the middle and lower layers were stable. The surface was continuously affected by the uniform pressure field or the top of weak inverted trough or the front of weak cold front, which provided a favorable circulation background for the continuous occurrence and development of fog-haze. The weak divergence, negative vorticity and weak downdraft in the boundary layer were the dynamic factors for the development of fog-haze weather. Long-time moisture saturation and low wind speed were beneficial to the occurrence and development of fog and haze. The average mixing layer height of fog was obviously lower than that of haze. The higher the haze level, the lower the height of the mixed layer. The change of mixing layer height was prior to the change of visibility, which was a guidance for the early warning of the fog-haze. The infiltration of weak cold air, proper increase of wind speed, rapid decline of mixing layer height and significant increase in the absolute value of negative net radiation exposure were the causes for the explosion of fog.