Yesterday (3.29.12) Megan and I met with Roy Heaton in Rhode Island’s Department of Health’s Air Quality devision to discuss development of low cost tests for hydrogen sulfide.
First we reviewed the experimental set up described in Horwell et al. 2004 for testing the photographic paper assay in laboratory conditions. I’ve made a diagram of the set up used by Horwell. In order to calibrate the photographic paper assay Horwell et al. exposed the photopaper strips to known quantities of Hydrogen Sulfide. They chose three concentrations of gas known to be measured in volcanic areas: 173, 926 and 3133 ppb (parts per billion). These concentrations were produced by diluting Hydrogen Sulfide gas mixtures prepared in cylinders at 10 ppm (parts per million) or 1000 ppm of H2S in air. These standards were diluted with purified air.
￼18 photo paper samplers were placed in the test chamber and 3 samples were removed at 6 different exposure times with the longest exposure time being 10 days.
Exposure times were 20 hrs, 99 hrs, 124 hrs, 147 hrs, 171 hrs and 200 hrs.
In this set up the concentration of H2S in the chamber is determined by the dilution of the H2S standard 10 ppm or 1000 pm by purified compressed air. The dilution is produced by mixing gases of known concentrations at known rates to meet a final concentration as expresses in this equation:
Concentration of span gas (flow of span gas/flow of dilution air) = final concentration
In this case:
10 ppm H2S = 10, 000 ppb H2S
10,000 ppb H2S(flow of span gas (H2S)/ 10, 000 cubic cm/min (Air)) = 173 ppb Flow of span gas (H2S) = 173 cubic cm/min
Reference for paper: Horwell, C.J., Allen, A.G., Mather, T.A., Patterson, J.E., 2004. Evaluation of a simple passive sampling technique for monitoring volcanogenic hydrogen sulphide. J. Environ. Monitor. 6, 630 - 635.