[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

753 atmospheric aerosol particulate pollutants in the

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7.5.3 Atmospheric Aerosol Particulate pollutants in the atmosphere consist of a mixture of suspended solid or liquid particles originating from different natural and anthropogenic
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Methodological Developments and Applications 621 sources. Knowledge of the chemical composition of atmospheric aerosol is re- quired for air quality characterization at a given location. The ultimate goal of aerosol studies is to determine the particle sources and to study the pos- sible physical and chemical processes occurring in the particles during their atmospheric transportation. The most common method to derive information about the sources is quantitative bulk analysis of particles collected sequen- tially onto filters, combined with factor analysis on the time or location vari- ance of the elemental concentrations [338]. The sources of air pollution have specific chemical fingerprints, source apportionment studies are also based on accurate knowledge on the chemical composition of the aerosol and its time variation. The chemical characterization of atmospheric particulate matter also provides an insight to the processes in atmospheric chemistry. Earlier air quality standards only regulated the mass of total suspended particulates (TSP), and concentration of some hazardous components without size fractionation. The atmospheric transportation behavior of the particles, however, strongly depends on their morphology and size. Also, the deposition of inhaled dust in the human respiratory tract is strongly dependent on the size and compositional distribution of the particles, since one particle hav- ing elevated concentrations of toxic elements can cause DNA change in one pulmonary cell, as a precursor of lung cancer [339]. The size of the particles can range form a few nanometers up to several 100 µ m [340], but for source apportionment studies the accumulation (respirable aerosol, 0.1–2.5 µ m) and sedimentation type particles (2.5–100 µ m) are the subject of study. The long range transport of heavy metal pollutants is mostly determined by particles smaller than 2.5 µ m (PM 2 . 5 ). In the past decade, however, limiting values were also reported for PM 10 , PM 2 . 5 (particulates of maximum 10 or 2.5 µ m aerodynamic diameter). For Eu- rope council directive 1999/30/EC set limiting values for PM 10 and lead in air [341]. For this reason, bulk analysis is mostly carried out on size-fractionated samples collected by stacked filter units or cascade impactors [342]. Several analytical methods are in use for chemical characterization of aerosols. As far as the elemental composition is concerned, XRF can provide partial analysis with a medium sensitivity. Its advantages are that it does not require difficult sample preparation, it is low cost and it is non-destructive. XRF spectroscopy is a useful analytical tool for determining the sample com- position down to trace concentration levels. The method is appreciated for its sufficient sensitivity, high dynamic range, non-destructiveness, and because of
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