Envlran. Sci. Technal. 1983, 17, 596-602
X-ray Diffraction Analysis of Airborne Particulates Collected by an Andersen Sampler. Compound Distribution vs. Particle Size Tsutomu Fukasawa, Masaakl Iwatsukl, and Sujlth P. Tlllekeratne
Department of Applied Chemistry, Faculty of Englneerlng, Yamanashi University, Commercially available Nuclepore and Fuji microfilters were used as the collection media in an Andersen sampler. After sampling, the filter with the particulates was dissolved in dichloromethane, centrifuged to reduce the amount of the filter material, and formed to a suitably small film for X-ray diffraction analysis. Preparation of the small-film sample, sample mounting on the diffractometer, recovery, reproducibility in the X-ray diffraction intensity, identification of compounds in the particulates, and construction of a compound distribution vs. particle size curve are described. The distribution curves of the compounds are also given for the particulates collected in dry and wet seasons as examples.
Introduction The Andersen air sampler (1) is used as a device to obtain the aerodynamic particle size distribution of airborne particulates. Many papers and reports have been published on the distribution curves of element concentration vs. particle size, which were determined by atomic absorption ( 2 , 3 ) ,neutron activation ( 2 , 4 ) ,and spectrophotometric analyses (3,5) of the particulates collected fractionally by the sampler. It has been reported ( 6 , nthat the X-ray diffraction analysis (XRD) of airborne particulates after heavy-liquid fractionation gave useful information for the study of air pollution. Also, the XRD has been carried out directly for the particulates collected by use of a dichotomous sampler (8) or for airborne heavy metals collected by a high-volume sampler in a zinc-lead smelter (9). No paper, however, has been published so far on the XRD of the particulates fractionated by the Andersen sampler or on compound distribution vs. particle size, although it is expected to provide more valuable information on the sources of pollutants, environmental chemistry, and others. Membrane filters can be used as the collection media mounted on the aluminum or glass plates in the Andersen sampler (14). The particulates, however, are dispersed as many spota on the collection media of 80 mm diameter and cannot be analyzed directly by using a cut piece of the medium by a conventional X-ray diffractometer because of its poor sensitivity. Therefore, the membrane filters with the collected particulates must be reduced to small-size films with all the particulates for the XRD. This paper describes the use of commercially available Nuclepore and Fuji microfilters (80 mm diameter) as the collection media, the preparation and reproducibility of small-size films (16 mm diameter) by using halogenated hydrocarbon, sample mounting on the goniometer, identification of compounds, construction of the distribution curves of compounds vs. particle size, etc. The identification of compounds was done by use of the JCPDS cards and the aid of the X-ray fluorescence analysis (XRF). The distribution curve of each compound vs. particle size was constructed by using its strongest diffraction line intensities from the film samples of all stages of the Andersen sampler and was compared with the distribution curves of the constituent elements vs. particle size obtained by using the results of the XRF of the same samples. Ex596 Envlron. Sci. Technol., Voi. 17,No. 10, 1983
Takedad,
Kofu-shl 400, Japan
Table I. Conditions of X-ray Diffraction Analysis X-ray tube voltage, kV current, mA filter d and s slit, deg
Cu 35 14 Ni 1
r slit, mm time const, s scan speed, deg/min chart speed, mm/min sample spin
0.6 4 1/2 5 on
Table 11. Conditions of X-ray Fluorescence Analysis
X-ray tube voltage, kV current, mA collimator detector analyzing cryst scan speed, deg/min chart speed, mm/min spinner path
heavy elements W 45 30 fine fc and sc LiF 1 5 on vacuum
light elements Cr 40 34 coarse fc EDDT 1 5 on vacuum
amples of the distribution curves of compounds vs. particle size are also given for the particulates collected in the dry winter and wet summer seasons. This method can be successfully applied to the analysis of any crystalline compound insoluble in the solvent, and the results obtained are very useful for environmental studies. Experimental Section Reagents, Filters, and Apparatus. All chemical reagents used were of analytical grade. An Andersen sampler, Koritau Model KA 200, consisting of eight stages with aluminum plates as collection supports was used for sampling. Nuclepore filters (pore size: 1,O pm, 80 mm diameter, 50 mg of polycarbonate, from Nuclepore Corp.) and Fuji microfilter FM-80(pore size: 0.8 Mm, 80 mm diameter, 210 mg of acetyl cellulose, from Fuji Photo Film Co. Ltd.)were used as collection media on the aluminum plates and backup filter, respectively. A constant-humidity box (type C-3, from Doi Co. Ltd.) was used for keeping moisture of samples constant. The humidity of the box was adjusted at 50% with 43% sulfuric acid. Samples were weighed with a Sartorius semimicro balance or a Cahn 26 automatic ultramicro electrobalance. A Rigaku X-ray diffractometer was used together with a standard rotating sample holder for the analysis of crystalline compounds, and the operating conditions are shown in Table I. A Philips PW 1410 semiautomatic X-ray spectrometer was used for the elemental analysis. The sample was placed between two nylon nets set in a standard aluminum holder in the case of heavy-element determination and between a tungsten mask (aperture: 10 mm diameter) and a nylon net set in the holder in the case of light-element determination. The operating conditions are shown in Table 11. Intensity measurements in the XRD and XRF were done by chart recording.
0013-936X/83/0917-0596$01.50/0
0 1983 American Chemical Society
Sampling. All filters were weighed after being kept in the 50% humidity box for 2 days before use (10). After the Nuclepore fiiters were mounted on the eight aluminum plates, they were arranged in order with a backup Fuji microfilter in the Andersen sampler. The sampling was done for around 10 days each, in a dry winter (Jan 12-23, 1982) and wet summer (July 2-13,1982) at a constant flow rate of 28.3 L/min on the roof of Applied Chemistry Department building at Yamanashi University. Calculation of Particle Size Distribution. After sampling, the filters were kept in the humidity box and weighed. Since the range of particle size varies on each stage, the simple histogram, with use of the weights of the Particulates collected and their particle sizes, cannot clearly show the distribution of the particulates. Therefore, first the accumulated weight percentage in each stage was calculated from the lowest (finest) to the higher (coarser) stages. In the conventional method, then, the curve of the accumulated weight percentage vs. particle size has been constructed by plotting the accumulated weight percentages vs. logarithm values of their particle sizes, and the weight distribution curve has been constructed by differentiating manually the curve on the figure. This manual differentiating, however, gives an additional personal error to the distribution curve. In a previous paper by us (11), however, the accumulated weight curve was constructed by substituting all the accumulated weight percentages and the logarithms of the particle sizes into the Lagrange interpolation equation (eq l),and the weight distribution
j=l j#i
JZk
curve was also directly constructed by substituting the accumulated weight percentages and the logarithms of the particle sizes into the differentiated formula (eq 2) of eq 1,without any personal error, respectively. In the equations, xi( x j ) is the logarithm of the particle size of the ith (jth) stage, yi is the accumulated percentage of the ith stage, n is the number of sets of data used for the interpolation, and x and y represent the logarithm of the arbitrary particle size to be interpolated and the interpolated value of an arbitrary accumulated percentage, respectively. Therefore, in the present paper, eq 2 was used directly with the interpolation of the fourth order (4 = n - 1)which was recommended (11) for the construction of the distribution curves. Sample Preparation and Mounting for XRD. Recommended procedure: Each filter with the particulates is dissolved in 10 mL of dichloromethane and centrifuged for 30 min at 2000 rpm in a 15-mL centrifuge tube with a cork stopper. After 9 mL is pipetted from the supernatant, the remainder is evaporated to obtain a deformed film with embedded particulates in the bottom of the centrifuge tube. The film is stripped off by use of a tweezer onto a 80-mm diameter watch glass that has a 16-mm diameter circle marked on the back-side, and a round homogeneous film of 16 mm diameter is made with the aid of a thin glass rod and a few drops of dichloromethane. Any filter material and particulates stuck onto the glass rod are transferred back to the sample by using a tweezer. The banks are also prepared in the same manner.
The sample film of 16 mm diameter is stuck onto a nondiffracting single-crystal quartz plate by using a drop of dichloromethane and mounted on the rotating sample holder of the diffractometer. This technique allowed to obtain a flat sample film suitable for the XRD and for sample rotation. Experiment for Recovery of Compounds and Reproducibilities of Small-Film Sample and Diffraction Intensities. Crystalline ammonium sulfate and chloride were found by the XRD in the particulates on the collection media, and the finding was supported by a chemical microanalysis (12).Therefore, these compounds were used for the test of recovery, reproducibility, and preferred orientation effect. Since dichloromethane was used for filter dissolution, its effects on these compounds were also studied, i.e., dissolution of the compounds, any change in the crystal shape, recrystallization, and others. Crystalline ammonium sulfate and chloride in powder form (
