Elemental composition of atmospheric particles during periods with and without traffic restriction in Beijing: The effectiveness of traffic restriction measure

In order to evaluate the effectiveness of air pollution control through traffic restriction measure, continuous atmospheric particle samples were collected using step sampler at an urban site in Beijing in August 2007 during traffic restriction and nonrestriction periods. Elements concentrations of aerosol samples were analyzed using Particle Induced X-Ray Emission (PIXE). As expected, the concentrations of most elements during the restriction period were considerably lower than those during the nonrestriction period. The concentration ratios of most dust elements such as Al, Si, Ca, Ti, and Fe between the restriction and nonrestriction periods were less than 0.3, indicating that the traffic restriction measure is an effective way in reducing soil dust trace elements in Beijing. The Enrichment factor (EF) values of elements Al, Si, K, Ca, Ti, Cr, Mn, and Fe were lower than 10 during both the restriction and non-restriction periods while EF values of other elements were in the range of 20-2000 during both periods. The EF values of Cl and Ni were lower during the restriction period compared to the non-restriction periods while the EF of S, Zn, As, and Br were higher during the restriction period. Soil dust concentrations during the traffic restriction period were only about 1/5 of those during the non-restriction period. These results suggested that traffic restriction is more effective on reducing dust elements concentrations, but less effective on reducing anthropogenic elements concentrations.