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The Fifth-Generation NCAR/Penn State Mesoscale Model (MM5) was used to simulate mixing layer height (MLH) andwind to understand the effect of their influence on pollution during a PM10 (particulate matter diameter less than 10um) episodeobserved in Changsha in January 2008 during the pollution episode time and two comparison times. The simulated surface winds andthe MLH are presented to contrast the characteristics of dispersion effect on no-episode and episode days. The results indicate that onepisode days the MLH and wind speed were lower than on no-episode day. It is believed that the low MLH value, as well as thesmall wind speed, contributed to high PM10 concentration. With the diurnal variation of mixing layer, wind speed and PM10concentration, we can deduce that the main meteorological factors contributing to the occurrence of PM10 episode was the extremelow MLH in night-time. The wind speed also makes important role in the formation of the pollution episode.