Abstract: Two continuous air pollution events on January 15 to 20, 2009 (called 0115) and on November 20 to 29, 2011 (called 1120) in Chongqing were compared.The results show that upper and lower situation with widespread descending current under 600 hPa is not favorable to precipitation when pollution intensity is stronger for the 0115 event.Atmosphere in boundary layer is in a static stability condition with multi-inversions in lower level under 1.5 km, and it is wet in upper level and dry in lower level for humidity vertical distribution.The surface is uniform pressure field;mean wind speed is 0.84 m·s^-1;the static wind frequency reaches 31.3%;turbulent fluctuation is weak because of small diurnal temperature range of 2.83℃.The severe fog or haze events (the minimum visibility is about 0.6 km) often happen in such a suitable atmospheric environment and the air pollution becomes more and more serious.On the other hand, duration of pollution is long for the 1120 event, and there is not precipitation.The circulation field in middle and lower level is narrow descending current.There are multi-inversions in boundary layer.Humidity distribution is dry in upper level and wet in lower level.The surface wind speed is 1.23 m·s^-1 and larger than that of 0115 event.The diurnal mean temperature range is 5.18℃ leading to stronger turbulent fluctuation in ground layer.Mean surface relative humidity is lower than 80.0%.It is mainly haze weather in this period.Duration of pollution is long, while concentrations of pollutants are relatively lower.

Key words: Air pollution, Atmospheric boundary layer, Temperature inversion, Relative humidity