The development of an ESEM based counting method for fine dust particles and a philosophy behind the background of particle adsorption on leaves

摘要

The multi scale benefits of urban greenery (green facades and green roofs) have attracted more and more interest of recent research work. The multi scale benefits of vegetation vary from; mitigation of the urban heat island effect, stimulation of the ecological value and biodiversity, aesthetical reasons and for example air pollution reduction. Air pollution control is at the moment mainly focussed on the reduction of fine particle concentrations. Particulate air pollution is damaging for the human health, it causes cardiovascular and lung diseases. Especially dust particles smaller than 2.5 micrometers are of great interest because they can be deeply inhaled into the respiratory system. To determine the effect of leaves on particle adsorption, micrographs are taken of ivy (Hedera helix) leaves using an Environmental Scanning Electron Microscope (ESEM). The examined leaves are exposed to a simulated rainfall in order to determine a method for particle counting on leaves and to determine the self cleaning effect of adsorbed particles on ivy leaves. The self cleaning effect is considered to be an important factor in the effectiveness of particle adsorption by leaves and the potential for resuspension of particles. Particles on pre- and post-rain leaves were counted via the ESEM micrographs using an image analyzer. Results showed that there is no significant effect on particle loss due to rain in the performed experiment. Our findings suggest that a strong Van der Waals bonding between　particle and leaf surface plays an important role in the retaining process of fine particles on the leaf surface.