北京市典型道路扬尘化学组分特征及年际变化

选择北京市具有代表性道路，于2004年9月和2013年5月进行采样，利用再悬浮设备制备道路扬尘PM₁₀与PM_2.5样品，并进行化学组分分析，建立了2004年和2013年北京市道路扬尘PM₁₀与PM_2.5源成分谱，以分析和探讨北京市道路扬尘化学组分特征及其组分年际变化.结果表明，北京市道路扬尘PM₁₀与PM_2.5源成分谱中的化学组分特征均为Ca、Si、有机碳（organic carbon，OC）、Al、Fe、K、Mg、SO₄^2-和元素碳（element carbon，EC），其在道路扬尘中的含量之和分别为：2004年PM₁₀为46.7303%、PM_2.5为56.9198%和2013年PM_2.5为38.7478%；占全部被测组分的比例分别为95.9%、94.3%和94.7%.2004年道路扬尘中，环路Si、Al的含量显著低于其他道路类型，受到的土壤风沙尘影响最小；建筑水泥尘特征元素Ca主干道含量最高，高速五环进京口含量最低；EC在高速五环进京口的含量显著高于其他道路类型.而2013年PM_2.5中被测组分总含量及Si、Al、Ca的含量次干道均显著低于其他道路类型.2013年与2004年相比，北京市道路扬尘PM_2.5中除SO₄^2-含量略上升了2.0%外，其余组分含量下降显著，Ca、Si、OC、Al、Fe、K、EC和NO₃^-下降幅度分别为45.1%、31.5%、17.5%、20.3%、55.6%、33.3%、30.0%和50.3%.结果表明，［NO₃^-］/［SO₄^2-］比值不能准确反映固定源和移动源相对贡献大小的变化.［OC］/［EC］比值，2004年PM₁₀为9.77±3.88，PM_2.5为9.36±3.25，2013年PM_2.5为14.41±10.41，北京市道路扬尘存在二次有机碳（secondary organic carbon，SOC），且SOC是道路扬尘PM₁₀与PM_2.5的重要组成部分.不同城市道路扬尘及同一城市不同粒径的道路扬尘成分谱相似度不高，应建立相应的成分谱并适时更新.

Characteristics and Interannual Variation of Chemical Components in Typical Road Dust in Beijing

Samples of road dust were collected from selected representative roads in Beijing in September 2004 and May 2013, and then re-suspended on filters using a NK-ZXF sampler to prepare road dust PM₁₀ and PM_2.5 samples. The concentrations of the chemical components in the road dust PM₁₀ and PM_2.5 were analyzed, and source profiles of the road dust in Beijing in 2004 and 2013 were established. The characteristics and interannual variation of the chemical components in the road dust in Beijing were analyzed and discussed. The results showed that the chemical components in the road dust PM₁₀ and PM_2.5 in Beijing were Ca, Si, organic carbon (OC), Al, Fe, K, Mg, SO₄^2-, and elemental carbon (EC). The total content of these chemical components in the PM₁₀ in 2004, PM_2.5 in 2004, and PM_2.5 in 2013 were 46.7303%, 56.9198%, and 38.7478%, respectively, and the total content of these chemical components accounted for 95.9%, 94.3% and 94.7% of the total content of all components tested, respectively. In 2004, the contents of Si and Al in the road dust of ring road were significantly lower than those of other road types, and the influence of soil dust on the ring road was the smallest. The content of Ca, a characteristic element of construction dust, was the highest in main road, and was the lowest in the expressway entrance to Beijing. The content of EC in the road dust from the expressway entrance to Beijing was significantly higher than that in other road types. However, in 2013, the total content of all components tested and the contents of Si, Al, and Ca in the road dust PM_2.5 of secondary main roads were significantly lower than those for other road types. Due to the implementation of dust, motor vehicles, and combustion source control measures in Beijing and the relocation of the Shougang corporation, only the content of SO₄^2- in the road dust PM_2.5 in Beijing increased slightly by 2.0% in 2013 compared with in 2004; the contents of the other components decreased significantly. The contents of Ca, Si, OC, Al, Fe, K, EC, and NO₃^- decreased by 45.1%, 31.5%, 17.5%, 20.3%, 55.6%, 33.3%, 30.0%, and 50.3%, respectively. The results showed that the ratio ofNO₃^-]/SO₄^2-] did not accurately reflect the changes in the relative contributions of fixed sources and moving sources. TheOC]/EC] ratios of PM₁₀ in 2004, PM_2.5 in 2004, and PM_2.5 in 2013 were 9.77±3.88, 9.36±3.25, and 14.41±10.41, respectively. Secondary organic carbon (SOC) pollution was present in road dust in Beijing, and the SOC was an important component in the road dust PM₁₀ and PM_2.5. The source profiles of different urban road dust samples and the source profiles of road dust of different sizes in the same city were not very similar, so the corresponding source profiles should be established and updated in a timely manner.