Indication To Urban Particulate Matter Pollution By Biomagnetic Monitoring

With the rapid development of economy and urbanization of China,air pollution has become more and more prominent,which has attracted wide attention from the scientific community,government departments and public.Among air pollutants,particulate matter pollution has become an important factor which leads to the death of our population,and effective monitoring of particulate matter can provide reference for improving air quality according to local conditions.Biomagnetic monitoring provides an economical and convenient and reliable way for the monitoring of urban particulate pollution in high spatial resolution.In present study,to evaluate the application of plant species with different dust retention capacities in urban particulate pollution monitoring,the interspecies variation,temporal-spatial variation and influencing factors of the mass of leaf-deposited particles and magnetic characteristics of urban common green plant species in Lanzhou City are analyzed.And then,the distribution of particles pollution on the vertical and horizontal scales that is recorded by leaf magnetism and the influencing factors are analyzed in an urban open road microenvironment.On a regional scale,the spatial distribution of urban particulate matter pollution with high spatial resolution are obtained.The main conclusions are as follows:?1?To assess which plant species are more suitable for urban particulate matter pollution monitoring,the mass of leaf-deposited particles and leaf magnetic characteristics of urban common green plants are analyzed.The results show that the mass of leaf-deposited particles,unwashed leaf magnetism?SIRM_u?and the difference of magnetism of unwashed leaf and washed leaf(SIRM_u-w)evergreen shrubs are significantly higher than other plant types.For each plant species,significant interspecies differences are observed in the mass of leaf-deposited particles,SIRM_u and SIRM_u-w.The highest and lowest mass of leaf-deposited particles are found for Buxus sinica and Berberis thunbergii,respectively.The mass of leaf-deposited particles,SIRM_u and SIRM_u-w are significantly higher in traffic areas than residential areas and parks,indicating that pollution sources and intensity have an important effect on the particles deposited on the leaf surface,and leaf magnetism is dominated by the mass of leaf-deposited particles,rather leaf itself which contribute less to the leaf magnetism.?2?In an open road environment?urban microenvironment?,the magnetic characteristics of the leaf-deposited particles are dominated by ferromagnetic minerals with the magnetic grain size of multi-domain?MD?.Significant correlations between SIRM_u-w and Ca,Fe,Al,Mn,Zn,Pb,Cu and Cd are found,indicate that the sources of magnetic minerals and heavy metals are the same.The mean EF of elements Zn,Pb,Cu and Cd are 10.72,10.45,5.19 and 4.02,respectively,which indicate the substantial enrichment of PM by anthropogenic pollutants.In general,the concentrations of Mn,Zn,Pb,Cu,Cd are mainly controlled by road traffic.One of the most frequent wind directions?NE?near the ground surface results in the accumulation of larger quantities on the tree leaves in the windward?NE?than that in the leeside?SW?,and the movement of vehicle has influence on the direction of pollutant transportation and dispersion.Road pollutants are mainly concentrated on the needles of rows of trees below 340 cm height?especially below 200 cm?on the sides facing the road.In addition,decreasing concentrations of pollutants are observed with increasing elevation above the road surface.In general,tree configuration is shown to be an important factor affecting the accumulation and diffusion of road pollutants in an open environment.?3?The magnetism of leaves along the road show significant orientation and seasonal changes,with the side facing to the road significantly higher than the opposite side?p<0.0001?,and leaf magnetism in winter significantly higher than the summer?p<0.0001?.The distribution of particle pollution in different orientation recorded by the leaf magnetism confirms the efficacy of the road trees as a green barrier,and the seasonal variation indicates the seasonal changes of urban air particulate pollution.?4?On a regional scale,based on the magnetism of leaves and street dust along the roads in seven major cities in Gansu Province?Lanzhou,Baiyin,Jinchang,Wuwei,Zhangye,Jiuquan and Jiayuguan?,urban particulate matter pollution distribution is mapped for each city.The results between cities show that leaf and street dust magnetisms in Lanzhou and Jiayuguan are significantly higher than other cities.Within each city,the SIRM of leaf and street dust successfully delineated areas of atmospheric particulate matter pollution.Jiayuguan northern Jiabei industrial park,eastern Jiadong industrial park near the emergence of pollution high-value centers;southeast of Jinchang where affected by smelters,southwest by mining areas,particle pollution distribution decreasing from southeast to northwest;Jiuquan and Zhangye have no obvious regional concentration of pollution distribution,high value centers are influenced by urban commercial activities,road nodes and other point pollution sources;in Wuwei,high value centers appear along the southern ring road,central commercial district and around a petrol station of northeastern;in Baiyin,high value centers and serious particulate pollution appear in the eastern industrial zone,along the southern G109 national highway and near the northern railway station;overall,the values in Lanzhou are high,with center of high values appearing at railway stations,Donggang,along major roads and in the western industrial areas.In general,pollution maps with high spatial resolution of urban particulate matter distribution could be obtained through the combined application of leaf and street dust SIRM.