Elemental analysis atmospheric aerosols

The chemical characterization of aerosol particles currently is of great interest in the field of atmospheric chemistry. A major goal is the development of a method for continuous elemental analysis of aerosols, especially for the elements C, N, and S. Chemiluminescence reactions described in this chapter have adequate sensitivity and selectivity for such analyses. In fact, considering that a 1- j.m-diameter particle has a mass of =0.5-1.0 pg, online analysis of single aerosol particles should be achievable, especially for larger particles. 

Sekera (1957) and Rozenberg (1960) emphasized the importance of measuring all matrix elements for atmospheric aerosols, and a few such measurements have been reported (Pritchard and Elliot, 1960 Beardsley, 1968 Golovanev et al., 1971). With sensitive modulation techniques it should indeed be possible to probe atmospheric particles remotely using the complete scattering matrix to infer not only size distributions but also refractive indices. Care must be exercised, however, because nonsphericity can lead to false inferences about absorption analysis based on Mie theory cannot disentangle the two effects. 

Bogen J. 1973. Trace elements in atmospheric aerosol in the Heidelberg area, measured by instrumental neutron activation analysis. Atmos Environ 7 1117-1125. 

Kasahara M, Takahashi K, Sakisaka M, Tomita M (1993) Standard samples and calibration of PIXE analysis. Nucl Instrum Methods Phys Res B 75 136-139 Kasahara M, Ogiwara H, Yamamoto K (1996a) Soluble and insoluble components of air pollutants scavenged by rain water. Nucl Instrum Methods Phys Res B 118 400-402 Kasahara M, Park JH, Chatani S (1996b) Size distribution and solubility of 15 elements in atmospheric aerosols. Int J PIXE 6 299-310... 

The existing variety of means and methods of micro-element analysis is used worldwide for the determination of element contents in atmospheric aerosols when they ai e collected at aspiration filters, sediment and natural surfaces and biota objects where toxic substances migration can be observed. 

The high heterogeneity with respect to the chemical nature and origin of the BC constituents means that various terms are nonspecifically applied for different fractions. For example, the term BC is used not only for the whole continuum (Masiello, 2004) but also more specifically for the more resistant fractions (Kuhlbusch, 1995 Alexis et al., 2006) the expression charcoal or char can be a synonym for the total burnt materials (Knicker et al., 2006) but can also describe more specifically the burnt material identified by visual assessment (Preston and Schmidt, 2006). The expression elemental carbon (EC) is used in association with the oxidation-resistant fraction in analysis of atmospheric aerosols and soot. The fraction remaining after chemical oxidation has been described as chemical-oxidation-resistant elemental carbon (COREC) (Bird and Grocke, 1997 Rumpel et al., 2006 Knicker et al.,... 

An inductively-coupled plasma (ICP) is an effective spectroscopic excitation source, which in combination with atomic emission spectrometry (AES) is important in inorganic elemental analysis. ICP was also considered as an ion source for MS. An ICP-MS system is a special type of atmospheric-pressure ion source, where the liquid is nebulized into an atmospheric-pressure spray chamber. The larger droplets are separated from the smaller droplets and drained to waste. The aerosol of small droplets is transported by means of argon to the torch, where the ICP is generated and sustained. The analytes are atomized, and ionization of the elements takes place. Ions are sampled through an orifice into an atmospheric-pressure-vacuum interface, similar to an atmospheric-pressure ionization system for LC-MS. LC-ICP-MS is extensively reviewed, e.g., [12]. 

The long-term goal of the chemistry of atmospheric aerosols is to establish analytical methods for determining the chemical composition of particular submicrometric particles. At the present time, this requirement is partially satisfied by two methods— electron and ion microprobes, which are based on the analysis of a point-concentrated electron or ion beam. By use of the ion microprobe it is possible to determine essentially all the elements, whereas the electron microprobe is suitable only for elemeiits with a greater atomic mass than sodium. 

Table 3.4 compares detection limits with secondary fluorescers to the results with the RMF method and 15-kV broadband excitation [16,17]. Four different fluorescence analyzers were tested (units A, B, C, and D), and the results were corrected for differences in performance for the energy-dispersive spectrometers employed on each unit. Unit A used a chromium anode tube, and unit B used a tungsten anode tube. Unit A was a commercial, general-purpose instrument. Unit B was specifically designed for atmospheric aerosol analysis, where closer coupling between the tube, fluorescer, sample, and detector could be employed with some sacrifice of insensitivity to specimen-positioning errors. Table 3.5 lists the x-ray tube operating conditions required for Table 3.4. For medium- to high-atomic-number elements, the secondary fluorescer method provides detection limits equivalent to the RMF element, but requires much higher x-ray tube power. For light elements.

From the earliest days of PIXE, biological applications have attracted much attention. The role of essential trace elements and correlations between the concentrations of these elements and different types of diseases have been widely studied. The more recent interest in environmental problems led to an increase in the use of PIXE. Since PIXE is an almost ideal technique for the multielement analysis of aerosols filtered out of the atmosphere, many... 

In multielement analysis, choosing the optimal irradiation, cooling, and counting conditions for each element is obviously not feasible, so a compromise must be found. The balance between working up a reasonable number of samples and the desired quality of the analytical results will dictate the mode of the irradiation-counting scheme. A typical scheme has been described for atmospheric aerosols (Fig. 3) [35]. For the shortlived radionuclides, irradiation of a 2- to 25-mg sample for a few minutes, together with a flux monitor, is employed. Typically, 10-15 elements are determined from this irradiation. Longer irra-... 

Neutron activation analysis is one of the major techniques for the determination of many minor and trace elements in a large variety of solid environmental and pollution samples, such as atmospheric aerosols, particulate emissions, fly ash, coal, incineration ash, and sewage sludge. Instrumental neutron activation analysis of total, inhal-able, or respirable airborne particulate matter collected on a cellulose or membrane filter, or in a cascade impactor on some organic substrate, allows the determination of up to 45 elements by an irradiation - counting scheme similar to the one given in Figure 3. Radiochemical NAA is applied only when extremely low limits of determination are required. Instrumental photon activation analysis is also complementary to INAA. 

Another major application area for quadrupoles is in ICP-MS systems for trace element analysis. A schematic of a system is shown in Figure 11. This ion source is an induction plasma in argon at atmospheric pressure with a temperature of 5000-7000 K contained in a torch. Samples are introduced to the plasma as aerosols, usually solutions that are sprayed. At the high plasma temperature dissolved solutes are vaporized, atomized and ionized. Most... 

For exposure of reasons of observable discrepancy of results of the analysis simulated experiment with application synthetic reference samples of aerosols [1]. The models have demonstrated absence of significant systematic errors in results XRF. While results AAA and FMA depend on sort of chemical combination of an elements, method of an ashing of a material and mass of silicic acid remaining after an ashing of samples. The investigations performed have shown that silicic acid adsorbs up to 40 % (rel.) ions of metals. The coefficient of a variation V, describing effect of the indicated factors on results of the analysis, varies %) for Mn and Fe from 5 up to 20, for Cu - from 10 up to 40, for Pb - from 10 up to 70, for Co the ambassador of a dry ashing of samples - exceeds 50. At definition Cr by a method AAA the value V reaches 70 %, if element presences an atmosphere in the form of Cr O. At photometric definition Cr (VI) the value V is equal 40%, when the element is present at aerosols in the form of chromates of heavy metals. 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

Johnson, R.L. Huntzlcker, J.J. "Analysis of volatilizable and elemental carbon in ambient aerosols", in "Proceedings Carbonaceous Particles in the Atmosphere", T. Novakov, Ed., Lawrence Berkeley Laboratory, Berkeley, California, June 1979, 10-13. 

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