Natural near field sinks of hydrogen sulfide from two geothermal power plants in Iceland

Hydrogen sulfide (H₂S) emissions have been growing with the increasing utilization of geothermal resources. Atmospheric H₂S concentration has been measured and studied but less is known about the natural sinks of the chemical. This study investigates the atmospheric depletion of H₂S within a 35km distance from two Icelandic power plants. The results showed that atmospheric oxidation by the OH radical was the largest sink in the area. The second largest sink was H₂S uptake in surface water, in a neighboring lake, but it was, however, small compared to the reported difference of sulfur amount in the lake in- and outflow. Sulfur was found to accumulate in moss close to the power plants at a maximum rate of about 1500mgS/kg moss per year and decreased exponentially from the source, being negligible at a distance of a few kilometers. Soil uptake was limited by diffusion of H₂S into the porous media and was thus much smaller than the estimated soil uptake potential. Washout with precipitation was estimated to be the smallest sink due to the low H₂S reactivity in the precipitation (pH=5.6), compared to the surface water (pH ~8). Depletion of H₂S from the atmosphere in the study area was estimated to be about 1.2% of the 2012 power plants emissions of over 20,000tons. Although the uncertainties in the depletion estimates were considerable, most of the H₂S emitted from the power plants was strongly indicated to be transported out of the study area as H₂S.