北京市道路灰尘中污染物含量沿城乡梯度、道路密度梯度的变化特征

采用网格布点法调查了北京市六环范围内220个样点道路地表灰尘样品中的污染物含量.探讨了样点缓冲区内单位面积道路节点数、道路密度和道路灰尘中污染物含量沿城乡梯度的变化特征及各指标间的相关性.结果表明,各指标在研究区内的变幅较大.沿城乡梯度,道路和污染物主要呈现3种变化趋势:①单位面积道路节点数,道路密度,Cu、Cr和Pb沿城乡梯度降低,且开始时降低较快;②Mn和Cd沿城乡梯度变化的程度较低,均值基本维持恒定;③自中心向外围,Ni和有机碳(TOC)、总氮(TN)先随距离波动降低,随后在郊区均值缓慢增高.道路灰尘中污染物含量趋势转折点位置均大致在距城市中心点15～20 km左右.相关分析表明道路指标和道路灰尘中的Cd含量不具相关性,总硫(TS)、Mn、pH的相关性较弱,与其他各元素的相关性排序为Cu>TN>TOC>Pb>Ni>Cr,较道路密度而言,单位面积节点数和各元素间的相关性更高,该指标可指示道路灰尘中Cu、TN、TOC、Pb、Ni、Cr元素污染.

Content Trends of Pollutants in Street Dust of Beijing Along the Urban-Rural Gradient and Road Density Gradient

In the article, pollutant content of 220 road dust samples within the sixth ring road of Beijing have been investigated by using grid stationing sampling method. The changing characteristics of road nude number per unit area, road network density and pollutant content within buffering areas along urban to rural gradient were also studied. Three following variation trends are presented as each index varies widely within the research areas. Firstly, road nude number per unit area, road network density and Cu, Cr, Pb content decrease along urban to rural gradient, and they decrease sharply in the beginning. Secondly, Mn, Cd content change a little along urban to rural gradient, and mean value remains stable. Thirdly, the content of Ni, TOC, TN decreases along with the distance fluctuations in the beginning and their mean values are then rising slowly in the suburbs. The turning point of pollutant content are found in places 15-20 km away from city center. The article shows that the road index and Cd content are irrelevant, and weak correlations are found between road index, TS, Mn and pH. And other relevance ranking are described as follows: Cu>TN>TOC>Pb>Ni>Cr. In contrast with road network density, higher correlations between road nude number per unit area and each element are fond, and element pollution of Cu, TN, TOC, Pb, Ni and Cr could be indicated by these indicators.