Elemental and ionic concentrations in the urban aerosol in Antwerp, Belgium

The results of a study of the elemental and ionic composition of the ambient aerosol in and around Antwerp are presented. Four sampling campaigns were performed, covering all seasons. The samples were obtained by filtration and impaction methods. Subsequently, the filters were analyzed by X-ray fluorescence spectrometry for elements, and the impactor substrates were leached with water and analyzed by ion chromatography for ions. When comparing the results of the chemical analysis with the meteorological information, it was found that the concentration of certain elements and ions in aerosol samples was affected considerably by the location of the sampling site and by the meteorological conditions. In relatively less polluted places like small towns and rural regions around Antwerp, the concentrations of some elements and ions showed qualitatively a positive or negative correlation in their time variations with the amount of precipitation. Hence, we suppose that in the first case these elements and ions are contained mainly in the more hygroscopic fraction (the most apparent is the behavior of Na and Cl), and that in the second case, the elements are mainly present in the less hygroscopic fraction of the ambient aerosol. However, this behavior of the elements and ions may be different for various particle size ranges. In the highly urbanized and industrial sites close to the central and industrial parts of Antwerp, these correlations were not found. This could be connected with the high and variable local aerosol generation rate, when only heavy rains are able to provide a sufficient removal of the aerosols from the atmosphere.