Mats Öblad

Application of an Energy Dispersive X-Ray Fluorescence Spectrometer to Air Pollution Studies

A secondary target Energy Dispersive X-ray Fluorescence spectrometer with three axial geometry has been used in multielement analysis of aerosols. A new type of monitoring system has been designed to monitor the flow of secondary photons and thus minimize the influence of time variation in the X-ray intensity. The aerosols were divided in two size fractions by means of a virtual impactor and deposited on filters. The absolute concentrations of the different elements were obtained by use of standard samples with known element concentrations. Detection limits for sixteen elements are given and are in the order of ng per cm2. The method has been applied to aerosols of widely varying composition and concentration in ambient atmosphere and industrial environment.

Analytical characterization of cytochrome oxidase preparations with regard to metal and phospholipid contents, peptide composition and catalytic activity.

A number of preparations of cytochrome oxidase have been analyzed for metals by energy dispersive X-ray fluorescence spectrometry. The EPR characteristics, the peptide compositions, the protein and phospholipid contents as well as the catalytic constants of the samples have also been determined. It is confirmed that the enzyme functional unit contains three copper atoms and one zinc atom in addition to two iron atoms. On the basis of the parameters determined for the different samples it is suggested that a high catalytic activity of a preparation can be correlated to a number of other analytical characteristics.

A study on the potential sources of air pollutants observed at Tjörn, Sweden.

The Potential Source Contribution Function (PSCF) receptor model combines both chemical and meteorological information. In this study, PSCF was employed to identify the potential source emission regions for aerosol compositions measured at Tjörn, Sweden (58.01 ∘N, 11.36 ∘E). PSCF was for the first time applied on a European scale. One hundred and fifty-two four-day air parcel backward trajectories were combined with concentrations of sixteen elements determined in 33 coarse and fine aerosol samples. The observations were made between February 17 and March 26, 1985. The modeling results of the heavy metals V, Pb, Zn, and As are presented and compared with available emission inventory data. A number of known industrialized regions in the former USSR and Europe are found of high potential to be the emission source areas. These areas are in good agreement with the known emission information. The PSCF maps of total sulfur, Non-Seasalt-Sulfur (N.S.S.) and chlorine are also presented. High potential regions in the Arctic area exist in the PSCF map for total sulfur wheres they do not occur in that for N.S.S.

Measurements of Br/Pb Ratios in Airborne Particles from Car Exhaust

Concentrations of particulate bromine and lead have been measured during one summer and one winter period. The measurements were made simultaneously in five sites in a city on the Swedish west coast. A rural site about 60 km from the city was used to measure the background aerosol. Aerosol sampling was made with six dichotomous virtual impactors, which fractionate the aerosol into two modes, one fine particle mode (aerodynamic diameter, a.d. < 3.5 μm) and one coarse particle mode (3.5 μm < a.d. < 18 μm). The aerosol was collected onto thin teflon filters. Element concentrations were obtained by Energy Dispersive X-Ray Fluorescence Analysis. The element concentrations were related to air mass trajectories. The Br/Pb ratio proved to be the same on a given date for the city sites and the background site. A dependence on the air mass history was found, suggesting that it is the quality of the air basin in the region that influences the Br/Pb ratio even for fresh car exhaust. The Br/Pb ratio was the same for fine and coarse particles, indicating that the ratio is determined before coagulation with larger particles occur. The ratios between coarse and fine particles containing lead and bromine respectively were also studied. The results suggest that lead and bromine are actually attached to the same particles.

Time and position dependent artefacts in X-ray spectra from a Si(Li) detector

The background levels in X-ray spectra from a Si(Li) detector have been studied in two different ways. First, an increasingly larger area of the detector was irradiated and significant changes in the resulting spectra were observed. Secondly, the detector was scanned across a diagonal and the detection efficiency was measured. Both methods showed that the active area as given by the manufacturer was significantly larger than that which could be irradiated without degradation of X-ray spectra. Furthermore, it is shown that the detector performance changed drastically with the time since the bias was applied. Artefacts and a general increase in the background reduced the usable detector area with 20% after twelve hours. In a normal analysis this gives rise to an increase in detection limits of up to 65% for an aerosol sample as compared to the detection limits when bias just has been applied.

Polarisation traps in a Si(Li)-detector

Time dependent background and artefacts in X-ray Fluorescence spectra have been studied with a fine X-ray beam close to the edge of the active area of a Si(Li) detector. The results indicate that polarisation takes place in this region of the detector under the influence of the bias. When the detector has been biased for several hours and is irradiated with photons in the 10-20 keV range the background decays with time constants in the order of 30 s and 1 h.

The dispersion of airborne particles from the city of Göteborg along a valley

Abstract Five virtual impactors have been used to sample airborne particles along a valley east of the city of Goteborg, Sweden. The instruments were placed so as to measure the transport and dispersion of particulate pollution from Goteborg. The collected samples were analysed with an EDXRF system. A brief comparison is made between the EDXRF and the PIXE methods. A quantitative estimate of the long range transported contribution to the concentration of the elements S, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br and Pb is given. The concentration gradients of the coarse and fine particles are discussed.

An improved X-ray technique for scanning the millimeter sized deposits from a multi orifice low pressure impactor

Abstract An X-ray spectrometer has been developed in order to study the spot shaped particle deposits from a multi orifice low pressure Berner impactor. The aim of this work was to develop a tool by which elemental mapping of the particle deposits can be made. The analysis is computer controlled so that the concentration for all detected elements can be automatically calculated. The X-ray beam has been strongly collimated and all distances between the sample, the X-ray source and the detector respectively have been minimised. Scanning can be done in both x- and y-directions in increments of 0.05 mm. For each step an ordinary EDXRF spectrum sampled during a live time of 1000 s has been shown to yield much better detection limits than an ordinary analysis. In addition to the use of a small X-ray beam pencil for scanning, the close geometry means improved sensitivities for all elements and especially for the lighter ones like Cl and S. A mapping of each deposit is time consuming and thus maybe not the method of choice for routine analyses of multi orifice impactor samples, but the elemental mapping is seen to be a good help when studying the performance of the impactor. This scanning can also be made regularly to check for changes in the characteristics of the impactor.