Role of Plant Leaves in Removing Airborne Dust and Associated Metals on Beijing Roadsides

As the capital of China, Beijing is continuously exposed to high amount of airborne dust, thus it is necessary to find improvement methods. Taking advantage of phytoremediation, an ecological and friendly way to improve air quality, this study investigates the role of urban plant leaves in removing airborne dust and its associated metals by analyzing leaf samples of 32 plant species in autumn. Results showed that leaves could remove dust from 0.510 to 23.0 g m(-2) with an overall mean of 7.50 g m(-2) on Beijing roadside sites. Some species removed certain metals more efficiently than others. Leaves of Chaenomeles speciosa accumulated the highest Cd (9.48 mu g g(-1)) and the highest Cr value (19.8 mu g g(-1)) was observed for leaves of Sorbaria kirilowii. Both of the highest concentrations of Cu (34.1 mu g g-1) and Fe (868 mu g g(-1)) appeared for leaves of Sophora japonica, whilst the highest values of Mn (169 mu g g(-1)) and Ni (18.7 mu g g(-1)) were found for leaves of Rosa chinensis and Prunus cerasifera f. atropurpurea, respectively. Populus beijingensis accumulated the most Pb (6.57 mu g g(-1)) and Populus tomentosa the most Zn (142 mu g g(-1)). For multi-metal pollution, Metal Accumulation Index (MAI) values were calculated, and the highest values were observed in unwashed leaves of Amygdalus persica (387), washed leaves of Punica granatum (105) and leaf dust of Viburnum sargentii (6.46). Plant species with dust accumulation rate above the mean including Koelreuteria paniculata, Ulmus pumila, Syringa oblata, Malus micromalu, Weigela florida cv. Red Prince, Ailanthus altissima, Salix babylonica, Robinia pseudoacacia, Ligustrum x vicaryi, Euonymus japonicus, Prunus cerasifera f. atropurpurea, Magnolia denudata, and species with higher MAI values including Amygdalus persica, Magnolia denudata, Syringa oblata are suggested to be considered in future green belt planning in Beijing.