Abstract:Based on the online observed concentration of H-1301, HCFC-22, CFC-11 and SF6 at Shangdianzi background station during 7—12 September 2012, a typical case about short-term fluctuation of halogenated greenhouse gases is analyzed by means of trajectory, footprint and flow field analysis methods.The trajectory analysis results show that, before occurrence of pollution, air masses mainly come from the further north and northwest at 1200 UTC 7 September 2012, with a long horizontal transport distance, rapid moving speed and high vertical height.Meanwhile, the corresponding volume fractions of halogenated greenhouse gases are relatively low, which are 4×10-12, 350×10-12, 260×10-12 and 10×10-12 for H-1301, HCFC-22, CFC-11 and SF6, respectively.However, in 9—10 September 2012, a certain percentage of air masses convolute over the south of the station with a short horizontal transport distance and low vertical height, moving slowly in the boundary layer, which hinders the spread of pollutants in the boundary layer and results in the relatively high concentrations of halogenated greenhouse gases.Such situation contributes a lot to the short-term rapid growth of concentration levels.The peak volume fractions of H-1301, HCFC-22 and CFC-11 reach 45×10-12, 1200×10-12 and 310×10-12 at 1200 UTC 9 September, respectively, and that of SF6 does 28×10-12 at 0300 UTC 10 September.On 11 September, the convoluting air mass in the southwest direction disappears.On 12 September, air masses all come from the far northwest and have rapid moving trajectories.The footprint analysis results are the same as the trajectory analysis results, which are that the regions with high sensitivity coefficient are mainly located in the north of the station in 7—8 September, and in the south of the station in 9—10 September.Then the regions with high sensitivity coefficients in the south of the station disappear in 11—12 September.In addition, the flow field analysis results show that the circulation pattern in 9—10 September is favorable for the accumulation of pollutants in the observed region, resulting in the short-term lift of pollutants' concentrations.