Atmospheric particles analysis

German M. S. and Buseck P. R. (1991) Automated scanning electron-microscopy for atmospheric particle analysis. Anal. Chem. 63, 2232-2237. 

Mathai (21) summarized the specialty conference on atmospheric visibility. With the exception of water content of particles and the measurement of organic species, analytical laboratory techniques are readily available for particle analysis. Regulatory approaches to mitigate existing visibility impairment and to prevent further impairment are being formulated. A... 

The chemical composition of particulate pollutants is determined in two forms specific elements, or specific compounds or ions. Knowledge of their chemical composition is useful in determining the sources of airborne particles and in understanding the fate of particles in the atmosphere. Elemental analysis yields results in terms of the individual elements present in a sample such as a given quantity of sulfur, S. From elemental analysis techniques we do not obtain direct information about the chemical form of S in a sample such as sulfate (SO/ ) or sulfide. Two nondestructive techniques used for direct elemental analysis of particulate samples are X-ray fluorescence spectroscopy (XRF) and neutron activation analysis (NAA). 

Cluster Analysis of Chemical Compositions of Individual Atmospheric Particles Data... 

K-means cluster analysis is an excellent method for the reduction of individual-partide datai if extra clusters are used to allow for the non-spherical shape and natural variability of atmospheric particles. The "merge" method for choosing seedpoints is useful for detecting the types of lew abundance particles that are interesting for urban atmospheric studies. Application to the Phoenix aerosol suggests that the ability to discriminate between various types of crustal particles may yield valuable information in addition to that derived from particle types more commonly associated with anthropogenic activity. 

Surface Chemical Analysis. Electron spectroscopy of chemical analysis (ESCA) has been the most useful technique for the identification of chemical compounds present on the surface of a composite sample of atmospheric particles. The most prominent examples Include the determination of the surface chemical states of S and N in aerosols, and the investigation of the catalytic role of soot in heterogeneous reactions involving gaseous SO2, NO, or NH3 (15, 39-41). It is apparent from these and other studies that most aerosol sulfur is in the form of sulfate, while most nitrogen is present as the ammonium ion. A substantial quantity of amine nitrogen also has been observed using ESCA (15, 39, 41). 

The chemistry of surfaces or interfaces is becoming increasingly important in a variety of scientific disciplines, including the environmental sciences. In the case of atmospheric particles, modern methods of surface chemical analysis are providing valuable insights into the chemical speclation, mechanisms of formation, sources, reactivity, and potential toxicity of pollutant species. 

In summary, there is relatively good agreement overall between different methods of elemental analysis for atmospheric particles, with many of the observed dis-... 

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. 

More ambitious attempts at measuring the heterogeneity of the atmospheric aerosol have been undertaken as well. Single-particle analysis by mass spectrometry was demonstrated by Sinha and co-workers (31, 32). In this technique, an aerosol sample is introduced into a vacuum chamber in the form of a particle beam. The particles are injected into a Knudsen cell oven, where they undergo many collisions with the cell wall and are ultimately vaporized and ionized. The ions are then mass-analyzed with a quad-rupole or sector mass spectrometer. So that individual particles can be analyzed, the flux of particles into the Knudsen cell is limited so that coincidence errors are minimized. Ion pulses from individual particles allow the determination of the amount of the species being analyzed in the particular particle. The sensitivity of the technique is limited. For sodium, the detection... 

Nevertheless, these methods all result in a filter that captures the atmospheric particles. The mass loading can be large, the deposit uniform, and the filter reasonably stable under transport to a central analytical laboratory. Numerous papers have treated analysis of such filters, so this information is not repeated. This chapter focuses on the problems of chemical analyses of impactor substrates, for which the problems are more serious and the solutions elusive. 

Beddows DCS, Dall osto M, Harrison RM (2009) Cluster analysis of rural, urban, and curbside atmospheric particle size data. Environ Sci Technol 43 4694-4700... 

Nowadays, thermo-optical methods are considered the most reliable measurement techniques for OC/EC split in atmospheric aerosols. Nevertheless, methods for TC/EC/BC analysis in atmospheric particles are still open to debate and their different analytical approaches have been the main cause for performing intercomparison studies (Schmid et al., 2001 ten Brink et al., 2004). The TC measurements showed good agreement, whereas the results of EC/BC determinations were highly variable due to EC overestimation by thermal methods. Furthermore, caution must be taken when using BC as an estimative of the EC content in aerosols, and vice versa BC and EC measurements are associated to the carbon content of colored and refractory organic compounds, respectively, which can lead to substantially different results between methods (Poschl, 2005). 

Sturges, W.T., Harrison, R.M. and Barrie, LA. (1989) Semi-quantitative X-ray diffraction analysis of size fractionated atmospheric particles. Atmos. Environ., 23, 1083-1098. 

Figure 2. Analysis sequence for chemical characterization of a particle on a substrate medium (a) XPS b) AES (c) ISS (d) SIMS. Copyright 1986. Electric Power Research Institute. EPRI TB.EAE.4.4.86 Atmospheric Particles [53], Reprinted with permission.

In this study we have employed the simultaneous collection of atmospheric particles and gases followed by multielement analysis as an approach for the determination of source-receptor relationships. A number of particulate tracer elements have previously been linked to sources (e.g., V to identify oil-fired power plant emissions, Na for marine aerosols, and Pb for motor vehicle contribution). Receptor methods commonly used to assess the interregional impact of such emissions include chemical mass balances (CMBs) and factor analysis (FA), the latter often including wind trajectories. With CMBs, source-strengths are determined (1) from the relative concentrations of marker elements measured at emission sources. When enough sample analyses are available, correlation calculations from FA and knowledge of source-emission compositions may identify groups of species from a common source type and identify potential marker elements. The source composition patterns are not necessary as the elemental concentrations in each sample are normalized to the mean value of the element. Recently a hybrid receptor model was proposed by Lewis and Stevens (2) in which the dispersion, deposition, and conversion characteristics of sulfur species in power-plant emissions... 

Present knowledge of the atmospheric aerosol and the limits of this review do not permit a detailed comparative analysis of the available variety and types of atmospheric particles, whose mechanisms of generation are both natural and anthropogenic. Therefore, proceeding from comparative data on the power of the sources of different kinds of aerosols... 

Kulmala M, Toivonen A, Ma kela JM, Laaksonen A (1998b) Analysis of the growth of nucleation mode particles observed in boreal forest. Tellus B 50 449-462 Kulrnala M, Piijola U, Ma kela JM (2000) Stable srrlpbadusters as a source of new atmospheric particles. Nature 404 66-69... 

To avoid possible contamination from atmospheric particles during sample manipulation and analysis, the equipment is installed in a clean chemistry laboratory, inside a Class 100 laminar flow area, or, during oceanographic cruises, under a laminar flow area in a clean ehemistry laboratory container (ISO20) available on board. 

Finally, the surfaces of the cores are examined both optically and by secondary electron microscopy to determine the extent of microstructural changes that are occuring due to atmospheric exposure. Energy dispersive analysis of x-rays (EDAX) also serves to detect atmospheric particles which have deposited onto the core surface. All this information can then be used to at least qualitatively identify deterioration processes that may be occuring. 

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