The atomospheric hydrogen sulfide at several ppb levels was determined by fluorometric method. This method is based on the fact that the presence of absorbed H2S quenches the fluorescence of the FMA (fluorescein mercury (II) acetate) solution. The method shows high sensitivity and reliability, and is suitable for the measurement of H2S at background levels. The range of determination of H2S is from- 0.1 to 10 ppb in sampling air volumes of 4l. Hydrogen sulfide is collected by passing the air through two bubblers, each containing 20 ml of 0.1N NaOH. More than 95% of atmospheric H2S can be collected by passing the air through two bubblers at the rate of 0.2l/min for 20 minutes. In summer 1975, the fluorometric method was used to measure atmospheric H2S at Hiyoshi, Yokohama. The result of these measurements is shown in Table 1. The average concentration of H2S during the sampling period was 2.7 ppb (102 measurements). The interesting phenomenon, that the concentration of H2S decreases during the daytime, was observed (Fig. 2). The concentration of H2S in the atmosphere, obviously relates to the weather conditions, temperature, humidity, and wind (Figs. 3 and 4). Under retained air conditions, high concentrations of H2S (4 or 5 times higher than the usual values) were measured (Table 3).
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