Magnetic Biomonitoring of Air Quality in Urban Environment Using Magnetic Properties of Tree Leaves: Effect of Tree Species

摘要

A magnetic biomonitoring study of air quality based on the magnetic properties of tree leaves was carried. A total of 200 tree leave samples were collected in same urban environment for determination of magnetic properties. Magnetic properties of leaves from different tree species from the same urban environment were compared. Magnetic susceptibility (χ) and saturation isothermal remnant magnetization (SIRM) of tree leaves ranged from 0.7 to 15.2×10-8m3/kg and 21.9 to 1510.6×10-6Am2/kg, respectively, which suggest the ability of trees leaves to accumulate urban dust particles from the atmosphere. Variability of magnetic properties between tree species was found to be significant. It was observed that leaves of pine tree (Cedrus deodara), Camphor tree (Cinnamomum camphora) and crytomeria (Cryptomeria japonica) present higher magnetic intensities than those of tree species, like oleander (Nerrium indicum Mill) and palm (Trachycarpus fortunei (Hook.)). The variations of magnetic susceptibility in the different tree species are interpreted in terms of the relative accumulation capacity of dust particles from the atmosphere. The magnetic susceptibility of tree leaves showed a strong linear positive correlation with the magnetic remanence of the tree leaves, suggesting common magnetic mineral carrier in urban dust on leaves. Environmental scanning election microscopy (ESEM) images revealed a complex particle composition of irregular shaped grains and spherules with a wide variation in size. Anthropogenic and vehicles derived particulates are responsible for tree leaf magnetism. The results indicate that a magnetic survey of tree leaves, which is relatively rapid, simple and inexpensive, may be used in addition to the classical air quality monitoring systems to identify and delineate high-polluted areas in urban environments.