Tracking magnetic pollutants by integrated mineralogical and magnetic analyses of airborne particles in urban environment

Zajzon, Norbert and Márton Péterné Szalay, Emőke and Sipos, Péter and Pethe, Mihály and Németh, Tibor and Kovácsné Kis, Viktória (2013) Tracking magnetic pollutants by integrated mineralogical and magnetic analyses of airborne particles in urban environment. Carpathian Journal of Earth and Environmental Sciences, 8 (4). pp. 221-229. ISSN 1842-4090; 1844-489X

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Abstract

This complex magnetic and mineralogical study, which was carried out on settled dust and PM10 (particulate matter smaller than 10 μm) samples collected for several years in a Hungarian industrial town, Miskolc. The primary aim of the research was to estimate the contribution of different pollution sources which produce magnetic phases to the settled dust and to the PM10 fraction. In both types of the airborne dust, magnetite a spinel type iron oxide was identified as the dominant magnetic mineral with magnetic and mineralogical methods. The latter revealed that the magnetic mineral was either pure magnetite or contained minor amounts, usually few percent in total of other metals like Mn (up to 2.2 at%), Zn (up to 4.6 at%), Co (up to 8.1 at%), Cr (up to 1.3 at%) and Pb (up to 0.5 at%). Comparison between the total magnetic susceptibilities of settled dust samples collected before and after the closing down, respectively of the steel works (DAM) in the town, reveals a significant reduction (50–100%) in magnetic pollution. Such comparison was not possible for PM10 fraction, since systematic PM10 collection in Miskolc started after the closing of DAM. The analysis of the PM10 filters was, however, important from the viewpoint of magnetic pollution originating from other sources, like vehicle traffic, combustion. We found that roughly the half of the magnetic particles are in the superparamagnetic range (< 30 nm), therefore extremely dangerous for the health. The degree of magnetic pollution shows daily and seasonal variations. The former points to vehicle traffic as a general source of magnetic grains, since the total susceptibility is lowest on Sundays (15*10-6 SI, till on weekdays ca. 20*10-6 SI). The seasonal variation indicates that industrial and household combustion increases the total susceptibility in winter time (from 5 to 8*10-6 SI in PM10). The mass of the PM10, however, increases much more (ca. 3 times) in wintertime than total susceptibility due to emission of large amount of non-magnetic particles, such as carbonaceous phases and sulphates from combustion sources. Thus, we think that restriction of vehicle traffic during wintertime is not an efficient measure to reduce the concentration of PM10 during smog alarm. Comparison between the concentrations of heavy metals (like Pb and Cd) and mass susceptibility lead to the conclusion that the magnetic pollutants and the metals are coming from different sources. The concentration of the latter depends on the direction and intensity of the wind, which may bring them form industrial sources, located North of Miskolc.

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