A turbidimetric technique using 2-aminoperimidine was investigated for the determination of sulfates in the atmosphere, and applied to the field measurement of sulfates. This method is simpler in procedure and is more sensitive and accurate than the conventional barium sulfate method. A suitable range of measurement of the method was from 0.5 to 5 ppm of sulfate concentrations in the solution, and the lower limit of detection was 0.2 ppm (Fig. 5). No stabilizing agents were required, since the turbidity due to the sulfate-reagent compound was very stable. The coefficient of variation in the measurements (n=5) was 4.0% for sulfate solution of 1 ppm (Table 1). The recommended procedures were as follows : the ambient aerosols were collected on a Millipore filter (AAWP 04700), and the sulfates in aerosols were extracted in distilled water, and filtered off. The filtrate was made up to 10 ml and 2 mi of 2-aminoperimidine (0.5w/v%) was added and the produced turbidity was measured at 600 nm (Fig. 1). The diurnal variation of sulfates concentration in ambient aerosols were observed at Hiyoshi, Yokohama-shi, in May, 1978. The coefficeint of variation of the analytical results was less than 10% (Table 3). This method made it possible to measure diurnal variation of sulfate concentrations in the atmosphere. The peak in the concentration of sulfates appeared in the afternoon, and its diurnal variation were similar to that of sulfur dioxide (Fig. 6).
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