Hydrogen sulfide volcanic emission

Sulfur forms several oxides that in atmospheric chemistry are referred to collectively as SOx (read sox ). The most important oxides and oxoacids of sulfur are the dioxide and trioxide and the corresponding sulfurous and sulfuric acids. Sulfur burns in air to form sulfur dioxide, S02 (11), a colorless, choking, poisonous gas (recall Fig. C.1). About 7 X 1010 kg of sulfur dioxide is produced annually from the decomposition of vegetation and from volcanic emissions. In addition, approximately 1 X 1011 kg of naturally occurring hydrogen sulfide is oxidized each year to the dioxide by atmospheric oxygen ... 

Natural emissions of sulfur compounds to the atmosphere occur from a variety of sources, including volcanic eruptions, sea spray, and a host of biogenic processes (e.g., Aneja, 1990). Most of the volcanic sulfur is emitted as S02, with smaller and highly variable amounts of hydrogen sulfide and dimethyl sulfide (CH3SCH3). Sea spray contains sulfate, some of which is carried over land masses. 

The fact that sulfur is often found in areas of volcanic activity may be due to the reaction of sulfur dioxide, S02, and hydrogen sulfide, H2S, both gases being found in volcanic emissions. One such reaction can be represented by the equation... 

Figure 1 A generalized geochemieal cycle for sulfur of the early 1970s. Note the large emissions of hydrogen sulfide from the land and oceans and that volcanic sulfur emissions are neglected (units Tg (s) a ...

Volcanic eruptions can cause some harmful health effects. Tourists were kept at some distance from the 2011 eruption of the Kilauea volcano (see Section 9.4.1) because of its emissions of sulfur dioxide gas. People may suffocate in the carbon dioxide or be poisoned by the toxic carbon monoxide and hydrogen sulfide. (If the geothermally active Yellowstone National Park in the United States was an industrial installation, it is likely that authorities would consider placing some areas off limits because of emissions of hydrogen sulfide, readily detected by visitors by its foul odor.) Fine particles blown into the atmosphere from volcanic eruptions can cause respiratory problems when inhaled. Plants may be killed or their growth stunted by exposure to sulfur dioxide and hydrogen sulfide from volcanoes. 

One of the representative applications of this SO2 sensor is the measurement of volcanic emissions. In this case, hydrogen sulfide gas will coexist with SO2, and its effect upon the sensor has been tested. The result is shown in fig. 55 (Adachi and Imanaka 1991). With H2S gas coexistence lower than approximately lOOOppm, the EMF value deviates to a lower value in comparison to the calculated (dashed) line. In this measurement, H2S is mixed with air with a fixed SO2 gas content. Therefore, H2S can be expected to be oxidized by the oxygen in the test atmosphere. The relation between the EMF output and the SO2 content is replotted in fig. 56 (Adachi and Imanaka 1991) as EMF vs. the total amount of SO2. The total amount corresponds to the sum of SO2 gas initially introduced and the SO2 gas produced by the oxidation, assuming that the introduced H2S gas is completely oxidized. The... 

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