Application of biomagnetic analysis technique using roadside trees for monitoring and identification of possible sources of atmospheric particulates in selected air pollution hotspots in Delhi, India

摘要

The present magnetic biomonitoring study was carried across different land use areas in some air pollution hotspots of Delhi using common roadside tree species Morus alba, Ficus religiosa, Ficus virens, and Ficus benghalensis to understand the magnitude and nature of the particulate pollution and possible sources by studying magnetic properties (magnetic susceptibility, frequency-dependent susceptibility, S-ratio, and SIRM) of the dust deposited on leaves. Mass specific magnetic susceptibility (10~(-8) m~3/kg) values were found to follow the order: Traffic intersection area (25.6-66.5) ＞ industrial area (25.4-41.3) ＞ residential area (13.2-30.1) ＞ institutional area serving as control (2.7-6.6). High magnetic susceptibility values indicated particulates with ferrimagnetic grains of anthropogenic or technogenic origin. Frequency-dependent susceptibility indicated dominance of coarse multidomain (MD) and pseudo-single domain (PSD) + MD grains in industrial area and major traffic intersection. Average S ratio across all study sites ranged from 0.92 to 0.99, indicating presence of soft magnetic mineral with low coercivity. High SIRM values (10~(-5) Am~2/kg) from 58.1 to 862.3 suggested prevalence of magnetite dominating atmospheric particulates, particularly in traffic intersection and industrial area and to some extent in residential area. Morus alba and Ficus religiosa were found more suitable biomonitors and the technique provided useful information on size, mineralogy, and the possible source of particulates.