Synoptic Analysis and Numerical Simulations of an Air Pollution Episode over Ningbo City in Winter

In order to study the influences of local pollutant source on the air quality of Ningbo city and the characteristics of meso-scale synoptic system which contribute to the formation of air pollution, an atmosphere pollution case in which air quality was higher than or equal to Level 3, which occurred during 19-27th Dec. 2006, is synoptically analyzed and simulated using the combined PSU/MM5 model with CALPUFF dispersion model with 1-km horizontal resolution, in which the local point source is considered. The results show that the main synoptic reasons for the haze episode were minimum altitude subsidence downdraught, temperature inversion layer, stable atmospheric layer, surface breeze or wind shadow under the control of high pressure or transformative high pressure ridge, and wind convergence line which is comprised of local circulations such as sea and land breeze, mountain and valley breeze, and urban heat island circulation. The simulation results indicate that the local source significantly influenced Ningbo area while moderate north-to-northeasterly winds were blowing because of the special basin landform of the area, that forecasting and warning of air pollution could focus on steering flow of 500-700hpa mean layer, and that air pollutant belt rotated clockwise against the background of weak wind.