Briant L. Davis

Airborne particulate study in five cities of China

Low-volume particulate samples (equivalent to PM10 size distributions) were taken during the fall and early winter of 1998–1999 in the cities of Dongying, Jinan, and Qingdao in Shandong Province, and in the independent districts of Shanghai and Beijing. X-ray diffraction and transmission analysis and polarizing optical microscopy were performed on the samples. The samples from all cities and districts contained the major components of quartz, feldspar, clays, calcium sulfates, and carbonates (except Qingdao). The Qingdao sample was surprising in that no carbonate components were observed. Carbonaceous matter dominated in all wintertime samples, but with a large variety of the mineral components also being present. It was also observed that some of the airborne calcium carbonate (calcite), an important fugitive dust constituent, reacted with sulfuric acid aerosols from industrial sources, to form two hydrated forms of calcium sulfate. The metastable carbonate, vaterite, was also observed in association with high-carbon samples, but its formation as an in situ reaction product is uncertain.

The quartz content and elemental composition of aerosols from selected sites of the EPA inhalable particulate network

Abstract The elemental composition and concentration of quartz in ambient aerosols collected on dichotomous filters from the EPA Inhalable Particulate Network (IPN) in 1980 have been determined by X-ray fluorescence and mass calibration methods of X-ray diffraction (XRD). Quartz concentrations were also determined by reference intensity ratio methods of XRD from high-volume (hi-vol) filters from ten U.S. cities and were compared with data obtained from the dichotomous samples. Twenty five individual sites are represented in the quartz analysis phase of the study. These analyses demonstrate that for all IPN sites, an average of only 4.9 (±2.3) weight per cent of the coarse particle mass as measured by the dichotomous samplers consists of quartz and 0.4 (±0.7) weight per cent as quartz in the fine fraction. Continental interior sites show the highest average quartz content as well as the greatest variability. Except for highly industrialized sites, the Coastal regions and Eastern interior sites reveal the lowest quartz concentrations. The quartz levels observed at Research Triangle Park, NC, Seattle, WA, and Portland, OR, are the lowest of the dichotomous data set, whereas those at Boston, MA, and Five Points, CA, represent the highest levels. The Si concentrations obtained from the quartz analyses were compared with Si measured directly by X-ray fluorescence on the same filters. The complete aerosol X-ray spectra from some samples such as Portland, OR, shows that the Si comes primarily from minerals such as feldspars, whereas the Si in the Buffalo, NY, aerosol comes primarily from quartz. The concentration of quartz combined with elemental composition and other crustal or anthropogenic constituents observed on the filters provides a means for developing unique geographical airshed signatures for use in detailed source apportionment studies.

Interlaboratory comparison of Receptor Model results for Houston aerosol

Abstract In exercises for the Mathematical and Empirical Receptor Models Workshop (Quail Roost II), nine investigators independently applied receptor models to apportion ambient aerosol mass concentrations to components from emission sources in Houston, TX. The receptor model results were based upon ambient aerosol compositional data supplied to investigators that included mass, elemental and ionic species concentrations for consecutive 12-h sampling periods at the University of Houston between 10 and 19 September 1980. Some investigators performed additional analyses by X-ray powder diffraction, scanning electron microscopy with automated image analysis and X-ray energy spectroscopy and light microscopy. In most cases, the fine (0.2–2.5 μm) and coarse (2.5–15 μm) fractions were analyzed separately by the receptor models. The models tested include effective variance type chemical mass balance, weighted ridge regression, multiple linear regression, factor analysis and target transformation factor analysis. The number of source classes determined ranged from 4 (by multiple linear regression) to 23 (by light microscopy). Results are presented and compared in eight general emissions categories.

X-ray diffraction analysis and source apportionment of Denver aerosol

Abstract Continuous sampling of airborne particulate matter at Commerce City in northeast metropolitan Denver was carried out for 3-1/2 days in late January 1982.The resulting low-volume and dichotomous filter samples were analyzed by X-ray powder diffraction, X-ray transmission and optical polarizing microscopy. Major species identified in the coarse fraction include quartz, clays, two varieties of feldspar (one, potassiumrich) and muscovite. Carbonaceous matter occurs primarily in the fine fraction where 52.9 % was observed in the dichotomous sample. Artifact sodium nitrate was observed deep within the fine fraction filter substrate of the dichotomous sample. A least squares effective variance source apportionment was applied to both sample sets yielding the following mass-weighted average source contributions: soil material, 47 %; salt aerosol from street standing, 5 %; normal vehicular combustion, 4 %; and local diesel emissions, 20.5 %. Also observed was 2.6 % nitrate of undefined source and approximately 1 % receptor mass, each from adjacent flour mill activities and a nearby coal-fired power plant.

“Standardless” X-ray diffraction quantitative analysis

Abstract An alternate derivation of Chungs (1974) equation for quantitative compound analysis by X-ray diffraction is presented, and verified from experimental data, to show that for most purposes, no internal standard need be added to a sample material during analysis. The reference intensity constant ( k Bi ) must be determined for all analyzed components, however, and internal standards must be used or special absorption measurements made for samples containing amorphous components.

On the use of various filter substrates for quantitative particulate analysis by X-Ray diffraction

Abstract Seven filter substrates, representing both fiber and membrane construction, have been studied for their utility in quantitative X-ray diffraction analysis. Filter material densities, indices of refraction, specific mass densities, mass absorption coefficients, and various properties relative to X-ray diffraction from the loaded filters have been determined. The degree to which these filters are suitable for quantitative X-ray diffraction is primarily dependent upon (1) interfering background scatter; and (2) the mass per unit area of the paniculate load collected. Teflon filters have proven to be superior to all others for specific mass loadings of less than 200 μg cm −2 . For mass loadings greater than 300μg cm −2 , the ‘quartz’ or glass fiber filters provide the most suitable substrate, primarily because of the better particle retention qualities and the lack of a substrate spectrum in the diffraction pattern.

Chemical and physical analyses of Houston aerosol for interlaboratory comparison of source apportionment procedures

Abstract Eighteen consecutive 12-h ambient aerosol samples were obtained in Houston, TX, as part of a U.S. Environmental Protection Agency visibility study in that city. The samples were collected on Teflon, Nuclepore and quartz filters by means of dichotomous samplers and were analyzed for mass, elemental and ionic species concentrations by β-ray attenuation. X-ray fluorescence, ion chromatography, colorimetry, instrumental neutron activation analysis and pyrolysis. The specimens and analytical data were distributed to participants of the Mathematical and Empirical Receptor Models Workshop (Quail Roost II), to provide a basis for comparison of source apportionment procedures. Certain workshop participants undertook further analyses of the specimens by X-ray powder diffraction, scanning electron microscopy with automated image analysis and X-ray energy spectroscopy and analytical light microscopy. This report describes all of these analytical procedures. Also, through prototype comparison mechanisms, the elemental, compound and individual particle data are reduced to a common basis (elemental composition), permitting intercomparisons of results from different methods. In general, the intercomparisons suggest that each analytical technique has certain advantages and limitations for receptor modeling and that the various techniques are best viewed as complimentary. Combinations of analytical approaches can lead to improved source resolution in the apportionment calculations.

Additional suggestions for X-ray quantitative analysis of high-volume filter samples

Abstract It has been observed that reference intensity constants for natural aerosols used in X-ray quantitative analysis of high-volume filter samples varies significantly according to the geological history and surface weathering conditions of the source rock or soil. Reference intensity values pertaining to compounds from actual geologic outcrops or soil types within the sampling area should be used in order for the highest accuracy to be obtained. Two “approximation” computations are suggested for circumstances where the more elaborate procedures involving matrix and transmission corrections may not be justified. The first, least accurate approximation, uses the Chung (1975) equation directly; the second and “better” approximation uses a simple beam transmission correction and the Chung equation in a one-step iteration. Very good agreement between the better approximation and the complete refinement procedure is observed for the several analyses presented.

Theory and application of X-ray diffraction compound analysis to high-volume filter samples

Abstract High-volume aerosol samples consist of very thin layers of aerosols embedded in glass fiber or cellulose filter material. Reliable quantitative analysis of material in such samples may be carried out only after appropriate correction for matrix absorption and masking by internal standards. A technique is described which permits analysis of all crystalline components of such collected aerosols by the addition of a thin layer of “reference” component followed by X-ray diffraction and analysis. The resulting intensities are corrected by the masking effect of the reference component, the absorption of the matrix, and the transparency of both reference and sample components. An aerosol suspension chamber has been constructed and used to simulate high-volume sample collection for verification of the correction theory and to provide a technique for adding the necessary reference intensity layer in actual high-volume filter analysis. A numerical example is presented which illustrates the successive steps required for intensity correction and weight fraction determination

A study of the errors in x-ray quantitative analysis procedures for aerosols collected on filter media

Abstract A large number of experimental variables are utilized in the X-ray quantitative analysis of crystalline and amorphous components of aerosols collected by air filtration methods. The individual errors associated with these variables can be combined statistically through use of an error expression applied to the basic analytical equations providing that either measurements of standard deviations or their estimates can be obtained. This procedure has been developed for the variables of X-ray mass absorption, aerosol load density, transmission and diffraction intensities, and reference intensity constants, and has been applied in the quantitative analysis of two filter samples containing both crystalline and amorphous components. The results indicate that, despite some subjectivity in estimating some of the required parameters, reasonable error magnitudes for the component weight fractions are obtained. By being consistent in the way one obtains the initial standard deviations for the input data, one may determine which of the variables most seriously affects the accuracy of the determined weight fractions. For the samples studied here, a marked sensitivity of the resulting weight fractions to reference intensity constants and aerosol load density is revealed.