Chemical speciation of chlorine in atmospheric aerosol samples by high-resolution proton induced X-ray emission spectroscopy Zsófia Kertész a, ⁎, Enikő Furu a , Matjaž Kavčič b, ⁎ a Institute of Nuclear Research of the Hungarian Academy of Sciences, Laboratory of Ion Beam Applications, H-4026 Debrecen, Bem tér 18/c, Hungary b J. Stefan Institute, Jamova 39, SI-1001 Ljubljana, Slovenia abstract article info Article history: Received 1 August 2012 Accepted 26 November 2012 Available online 5 December 2012 Keywords: Chemical speciation High-resolution PIXE spectroscopy Chlorine Atmospheric aerosols Chlorine is a main elemental component of atmospheric particulate matter (APM). The knowledge of the chemical form of chlorine is of primary importance for source apportionment and for estimation of health ef- fects of APM. In this work the applicability of high-resolution wavelength dispersive proton induced X-ray emission (PIXE) spectroscopy for chemical speciation of chlorine in fine fraction atmospheric aerosols is stud- ied. A Johansson-type crystal spectrometer with energy resolution below the natural linewidth of Cl K lines was used to record the high-resolution Kα and Kβ proton induced spectra of several reference Cl compounds and two atmospheric aerosol samples, which were collected for conventional PIXE analysis. The Kα spectra which refers to the oxidation state, showed very minor differences due to the high electronegativity of Cl. However, the Kβ spectra exhibited pronounced chemical effects which were significant enough to perform chemical speciation. The major chlorine component in two fine fraction aerosol samples collected during a 2010 winter campaign in Budapest was clearly identified as NaCl by comparing the high-resolution Cl Kβ spectra from the aerosol samples with the corresponding reference spectra. This work demonstrates the fea- sibility of high-resolution PIXE method for chemical speciation of Cl in aerosols. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Urban atmospheric aerosol pollution is one of the leading environ- mental problems. In order to work out effective mitigation strategies the knowledge of atmospheric particulate matter (APM) sources is essential. Atmospheric aerosols are a complex mixture of particles suspended in the air. Different emission sources can be described by characteristic chemical composition or characteristic elemental ratios [1]. Commonly applied analytical methods for the determination of the composition of APM are ion and gas chromatography, ICP-MS, ICP-OES, instrumental neutron activation analysis (INAA), and Fourier transform infrared spectroscopy (FTIR) [1]. For the determination of major, minor and trace element content of aerosol samples collected on filters nondestructive nuclear techniques like PIXE and X-ray fluo- rescence (XRF) are widely used [1,2]. The advantages of the PIXE method are that it requires very little sample preparation and pro- vides absolute, quantitative concentrations for elements between Mg and U without using any internal or external standards. However, this method yields elemental composition only but it is not sensitive to the chemical environment of the X-ray emitting atom and conse- quently it cannot provide the chemical speciation of APM compo- nents which is of primary importance in source characterization [3]. In order to determine chemical composition, statistical analysis performed on large database of measured samples is usually employed to look for correlations between particular components [4]. However, this approach provides only average chemical composition characteris- tic of the majority of the samples, and does not give information about individual events. Single particle analysis employing proton or electron microprobes [5–7] is another method used to determine chemical com- position. In this case the statistical analysis is performed on a database of individual aerosol particles measured on a particular sample [8]. This method is expensive, time consuming, and there is limitation in the size of the particles. Generally 0.4–0.5 μm is the smallest particle size which can be studied this way [5], whereas the majority of accumu- lation mode particles have an aerodynamic diameter between 0.1 and 0.5 μm [9]. In addition, light elements (H, C, N, O) and their compounds are often not included in the analysis due to the limitation of the analyt- ical techniques or the background originating from the support material. Alternatively, chemical characterization of a (single) bulk sample can be performed by high-resolution PIXE method employing wave- length dispersive X-ray (WDX) spectroscopy. The influence of the chemical environment is reflected in energy shifts of the characteris- tic lines, formation of satellite lines and changes in the emission linewidths and relative intensities. If we can push the experimental resolution towards the natural linewidths of the measured lines, it is feasible to make a chemical state analysis of bulk aerosol samples. In this case, the limiting factor is the sensitivity of the method, Spectrochimica Acta Part B 79–80 (2013) 58–62 ⁎ Corresponding authors. E-mail addresses: kertesz.zsofia@atomki.mta.hu (Z. Kertész), matjaz.kavcic@ijs.si (M. Kavčič). 0584-8547/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sab.2012.11.009 Contents lists available at SciVerse ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab