Ammonia sometimes present in geothermal steam increases the solubility of hydrogen sulfide in the steam condensate produced by the surface condenser in a steam cycle geothermal power generating unit by reacting with the hydrogen sulfide to produce nonvolatile ammonium bisulfide. The condenser vent gas also produced contains carbon dioxide. Contacting the steam condensate with the condenser vent gas at a pressure slightly greater than atmospheric causes carbon dioxide to dissolve in the condensate, decreasing pH and converting bisulfide ion back to hydrogen sulfide. Subsequently exposing the acidified condensate to condenser vacuum strips the hydrogen sulfide from the condensate, eliminating the need for further chemical treatment of the condensate to prevent air pollution. Hydrogen sulfide partitioning performance is further improved by converting the hydrogen sulfide in the vent gas to sulfur dioxide before contacting it with the condensate.