[H-GG02] Dialogues on natural resources and environment between earth and social sciences

[HGG02-02] Magnetic biomonitoring of the spatial distribution of atmospheric particulate matter in Toyama City, Toyama, Japan using Japanese flowering cherry

*Kana Otomura¹, Kazuo Kawasaki¹, Keiji Horikawa¹ (1.University of Toyama)

Keywords:Environmental magnetism, Atmospheric magnetic particles, Traffic volume, Japanese flowering cherry, Toyama

Magnetic biomonitoring techniques have been shown to be rapid, cost-effective and useful methods for investigating spatial distribution of urban air pollution. Here, environmental magnetic results are reported for the materials deposited on the Japanese flowering cherries (Prunus subgenus Cerasus). Our aims are to test the leaves' representativeness and to estimate temporal and spatial distributions of atmospheric particulate matter in Toyama City, Toyama, Japan. About three leaves were collected from each flowering cherry at a height of ~2.0 m from the ground and then collected leaves were put into 7 cm³ non-magnetic plastic cubes for magnetic analyses. Also the materials deposited on the top of the leaves were wiped off at selected sites and analyzed by low temperature experiments. First, a sample of leaves was collected every 20° around one flowering cherry tree located away from the road at the Jike Park in Toyama City. The distribution of saturation isothermal remanent magnetization (SIRM) intensities shows no significant difference between the sampling positions of the leaves around the tree, indicating that the effect of the sampling position in a tree is minimal. Second, leaves were collected at 81 sites in Toyama City in 2023. Detailed rock magnetic analyses indicate that the main magnetic minerals in the dust on the leaves are single-domain partially oxidized magnetite, and the magnetic mineralogy on the leaves’ surface is likely consistent throughout the study area. Higher SIRM intensities are observed in the urban area than in the rural area within Toyama City. The same trend has been observed over the past three years, indicating that the source of magnetic minerals in atmospheric particulate matter in Toyama City has been the same. Traffic volumes near the sites are roughly estimated by image analysis of photos taken by 57 traffic monitoring cameras in Toyama City, and most of the observed SIRM intensities show a weak positive correlation with the estimated traffic volume. Analysis of 12 elements on the surface of the leaves by ICP-MS showed no positive correlation with the observed SIRM intensities. These results indicate that magnetic biomonitoring using the leaves of the Japanese flowering cherry can be a rapid and cost-effective method for studying the spatial distribution of fine magnetic minerals derived from local traffic and/or industrial activities.