Hydrogen sulfide ambient concentrations

Hydrogen sulfide is a colorless, flammable gas at ambient temperature and pressure. It is an irritant and asphyxiant and has an offensive odor similar to rotten eggs. It has been reported that people can smell hydrogen sulfide at concentrations as low as 0.5 parts per billion (ppb) of air (ATSDR 1999). Hydrogen sulfide has an odor threshold of 0.02-0.13 parts per million (ppm) (Beauchamp et al. 1984). Olfactory fatigue (which causes a loss of odor perception) can occur at 100 ppm, and paralysis of the olfactory nerve has been reported at 150 ppm (Beauchamp et al. 1984). The chemical and physical properties of hydrogen sulfide are summarized in Table 7-1. 

Hydrogen sulfide levels in air on some NPL sites ranged from 0.9 to 808 ppm (HazDat 1997). Data on ambient air concentrations at all NPL sites were not available, however. 

The TLV-TWA for hydrogen sulfide gas is 10 ppm. Hydrogen sulfide gas is stored in a tank at 100 psig and 80°F. Estimate the diameter of a hole in the tank leading to a local hydrogen sulfide concentration equal to the TLV. The local ventilation rate is 2000 ft3/min and is deemed average. The ambient pressure is 1 atm. 

A dramatic departure of ozone measurements from total oxidant measurements has b Mi reported for the Houston, Texas, area. Side-by-side measurements suggested that either method was a poor predictor of the other. Consideration was given to known interferences due to oxides of nitrogen, sulfur dioxide, or hydrogen sulfide, and the deviations still could not be accounted for. In the worst case, the ozone measurements exceeded the national ambient air quality standard for 3 h, and the potassium iodide instrument read less than 15 ppb for the 24-h period. Sulfur dioxide was measured at 0.01-0.04 ppm throughout the day. Even for a 1 1 molar influence of sulfur dioxide, this could not explain the low oxidant values. Regression analysis was carried out to support the conclusion that the ozone concentration is often much higher than the nonozone oxidant concentration. 

For determing the concentration of hydrogen sulfide in the product gas, a Gow-Mac thermal conductivity cell (Model 10-952) was used. The cell was equipped with four matched pairs of AuW filaments, especially used because of their resistance to corrosion from the hydrogen sulfide. Layers of styrofoam were used to insulate the cell from changes in ambient temperature. This detector was found to be very sensitive to changes in the flow-rate. 

The Lurgi Purisol process [663], [717], [718], [726] uses AT-methylpyrrolidone (NMP) as solvent and can be operated at ambient temperature or, with inclusion of a refrigeration unit, at temperatures down to -15 °C. The bbS/CO-, selectivity is superior to Selexol, permitting the production of a rich Claus gas with about 50% H2S even at relatively low concentration of hydrogen sulfide in the raw gas. The solubility of COS is only 20% of that of H2S, but it is largely hydrolyzed by the NMP. Preferred operating pressure is 45 to 85 bar. The process can, of course, be... 

Hydrogen sulfide was released intermittently from an industrial source in the City of Terre Haute, Indiana, over a period of 2 months. Ambient air concentrations were reported to range from 0.002 to 8 ppm ( 0.0028-11 mg m ). Twenty-seven residents complained of nausea, headache, shortness of breath, sleep disturbance, and throat and eye irritation during this time. 

Conversion of Hydrogen Sulfide to Elemental Su ur. The form of sulfur that is thermodynamically stable at ambient conditions is the rhombic form, Sg. One of the most plausible sulfur precipitation mechanisms involves the formation of polysulfides (S,, where x = 2-S) along with elemental sulfur. The 84 and Ss polysulfide species are likely to predominate at the pH and HS concentration typical of the Stretford liquor (Giggenbach, 1972). 

Hydrogen sulfide at levels well above ambient concentrations destroys immature plant tissue. This t5 e of plant injury is readily distinguished from that due to other ph5dotoxins. More-sensitive species are killed by continuous exposure to around 3000 ppb H2S, whereas other species exhibit reduced growth, leaf lesions, and defoliation. 

---