In the winter, 1975, measurements of the concentrations of sulfur compounds (SO2, SO3 and H2S) in the atmospheric air were made in Yokohama area for the purpose to investigate the behaviors of these gases. The concentration of SO2 was measured by the p-rosalinine-form-aldehyde modified method, that of SO3 by turbidimetry with barium sulfate, and that of H2S by fluorometric method which is highly sensitive and suitable for the measurement of H2S on environmental levels. The results of the measurement are shown in Table 2. The average values within this period were 43.6 ppb (SO2), 10.9 ppb (SO3), and 0.87ppb (H2S). The relative concentration ratio of these sulfieds in the atmospheric air was 79: 19.2: 1.8. An interesting relation was observed between the concentration of SO2 and that of H2S; the concentration of H2S decreased in the daytime while that of SO, increased (Table 3 and Fig. 1). In the morning (10; 00), SO2/H2S concentration ratio was almost constant (30), But, during daytime (13; 00 and 16; 00) SO2/H2S concentration ratio was high and the range was great (50~200), In the evening (19; 00), the concentration of SO, decreased and concentration ratio became 30~100 (Fig. 2 and 3) again. SO2/SO3 concentration ratio was almost the same for varied concentrations of SO2 (Fig. 4) in the atmospheric air, while SO2/H2S concentration ratio increased with increasing concentration of SO2. Therefore, it was presumed that H2S might be emitted from the natural sources despite SO2 and SO3 were emitted from the common industrial sources.
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