Two-year magnetic monitoring in conjunction with geochemical and electron microscopic data of roadside dust in Seoul, Korea

doi:10.1016/j.atmosenv.2007.05.050

Atmospheric Environment

Volume 41, Issue 35, November 2007, Pages 7627-7641

https://doi.org/10.1016/j.atmosenv.2007.05.050 Get rights and content

Abstract

Mineral magnetic properties of roadside dusts in Seoul, Korea, were measured and compared with the results of geochemical analyses in order to investigate the spatio-temporal patterns of urban pollution. Scanning electron microscope (SEM) observations and energy dispersive X-ray spectroscopy (EDS) analyses were carried out to verify the magnetic materials and their potential sources. A total of 1956 dust samples were collected monthly at eight sites, from June 1998 to June 2000. Thermomagnetic data and SEM observations for magnetic extracts indicated that the major magnetic phase was magnetite-like material. In particular, the highest and the lowest magnetic concentrations were observed in industrial areas and a park area, respectively, whereas, heavy traffic areas showed low to intermediate concentration. A linear correlation between enrichment indexes of magnetic susceptibility and heavy metals suggests that magnetic susceptibility can be used as a proxy for heavy metal pollution. The magnetic concentrations and magnetic particle sizes showed systematic seasonal fluctuations (high and large in winter versus low and small in summer) due to the seasonal influx variations of anthropogenic magnetic materials. On the basis of the morphology and elemental composition, the magnetic materials were grouped into three types: magnetic spherules possibly emitted from factories and domestic heating systems, aggregates derived from vehicle emission or motor vehicle brake system, and angular magnetic particles of natural origin.

Introduction

Magnetic materials in urban environments are mainly derived from the combustion of fossil fuels (Flanders, 1994; Matzka and Maher, 1999; Muxworthy et al., 2001), abrasion/corrosion of brake lining (Österle et al., 2001) and the erosion of asphalted roads (Hoffmann et al., 1999), which are generally accompanied by hazardous heavy metals (Beckwith et al., 1986; Charlesworth and Lees, 1999; Shu et al., 2001). Due to their anthropogenic origin and close association with heavy metals, magnetic materials are considered an important pollutant in urban environments. Recently, magnetic measurements of various environmental materials, such as atmospheric particulates, roadside dust, soil and vegetations, have been successfully applied to determine the extent and source of pollution in many urban and industrial areas (e.g., Hoffmann et al., 1999; Muxworthy et al., 2001; Hanesch et al., 2003; Jordanova et al., 2003). Using the rapid and inexpensive magnetic method, it is possible to obtain qualitative or semi-quantitative data on urban pollution, such as the level, extent and source of pollution. Even though geochemical analyses provide quantitative data on urban pollution, they are fairly time-consuming and expensive. Therefore, the magnetic measurement in conjunction with a minimal geochemical analysis can be the most effective method to trace anthropogenic pollution.

Geochemical studies on heavy metal pollution in Seoul have recently been performed (e.g., Yun et al., 2000; Lee et al., 2005). These studies have proposed that heavy traffics and industrial activities are the major sources of heavy metal pollution. However, the seasonal variations in heavy metal pollution are not sufficiently understood. The major aim of this study is to examine the spatio-temporal variations in anthropogenic pollution within Seoul, based on the monthly based monitoring of magnetic properties of roadside dusts. In order to clarify the source(s) of pollution, detailed geochemical, magnetic and microscopic investigations were carried out for 2 years.

Section snippets

Study area and sampling

Seoul is located in the west-central part of the Korean Peninsula (Fig. 1). The meteorological conditions in Seoul are typically influenced by the East Asian monsoon. Korean summer months (from June to August) are hot (average 24 °C), humid (average rainfall of 270 mm month⁻¹) and dominated by southeasterly or southwesterly winds. Conversely, winter months (from December to February) are cold (average −1 °C), dry (average rainfall of 24 mm month⁻¹) and characterized by a northwesterly wind (KMA, 2000

Experimental methods

Various magnetic properties of the collected dust samples were measured to discriminate the concentration, grain size and mineralogy of magnetic materials. Mass magnetic susceptibility (χ) was measured at a frequency of 0.47 kHz using a Bartington MS2 magnetic susceptibility meter. Anhysteretic remanent magnetization (ARM) was induced in a peak alternating field (AF) of 90 mT with a steady field of 0.05 mT using a Molspin AF demagnetizer with an ARM attachment. Isothermal remanent magnetization

Magnetic mineralogical properties

The S-ratio reflects a relative proportion of high-coercivity canted antiferromagnetic minerals (e.g., Fe₂O₃) to low-coercivity ferrimagnetic minerals (e.g., Fe₃O₄) (Thompson and Oldfield, 1986; Evans and Heller, 2003). High S-ratio (near 1.00) indicates a prominence of ferrimagnetic minerals. For the dust samples from Seoul, the mean S-ratio was about 0.95, suggesting a predominance of ferrimagnetic minerals (Table 1). In addition, selected samples showed a rapid increase of IRM with nearly

Sources of magnetic materials in dusts

In the city of Seoul, particulate emissions from diesel-powered vehicles are estimated to be 8800 ton day⁻¹, while those from unleaded gasoline- and LPG-powered vehicles are negligible (SMG, 2002). To identify the magnetic materials derived from vehicle emission, SEM observations were performed on the magnetic extracts from particulates gathered by a dust collector (bag filter type) from diesel-powered vehicle emissions. Most magnetic particles derived from vehicle emissions were identified as an

Summary

This study has successfully delineated the spatio-temporal pollution features in Seoul. Spatially, both the magnetic concentration and heavy metal concentration in dusts were highest in an industrial area, and lowest in a park area. Significant correlations between EI_χ and EI_metals confirm the validity of the use of magnetic parameters as efficient environmental proxies of heavy metal pollution. Temporally, the influx rates of anthropogenic particulates increase during the cold and dry winter

Acknowledgments

This study was financially supported by the Environmental Geosphere Research Lab (EGRL) of Korea University. The manuscript was greatly improved by Dr. Y. Yu, Dr. S. Timmis and an anonymous referee.

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Two-year magnetic monitoring in conjunction with geochemical and electron microscopic data of roadside dust in Seoul, Korea

Abstract

Introduction

Section snippets

Study area and sampling

Experimental methods

Magnetic mineralogical properties

Sources of magnetic materials in dusts

Summary

Acknowledgments

Physics of the Earth and Planetary Interiors

Atmospheric Environment

Journal of Geochemical Exploration

Earth and Planetary Science Letters

Journal of Applied Geophysics

Journal of Aerosol Science

Atmospheric Environment

Chemosphere

Palaeogeography Palaeoclimatology Palaeoecology

Atmospheric Environment

Environmental Pollution

Wear

Applied Geochemistry

Atmospheric Environment