Spatial and temporal evaluation of H2S, SO2 and NH3 concentrations near Cerro Prieto geothermal power plant in Mexico

Abstract Power generation is associated with toxic emissions. Hydrogen sulfide (H2S) and ammonia (NH3) are toxic gases emitted from geothermal power generation that have negative impacts on health and the environment. Oxidation of H2S leads to formation of SO2 that also has health and environmental effects. The Cerro Prieto geothermal power plant (CP-GPP) is one of the largest in the world and is located 30 km south of Mexicali, a border city between Mexico and the US. Power from this plant is sold to both countries. In order to assess the potential effects of the emissions from the GPP on nearby low-income communities, H2S, SO2 and NH3 concentrations were measured at Nuevo Leon, El Chimi, and Estacion Delta, using passive samplers from November 2013 to June 2014. The highest concentrations of H2S were recorded during periods of high atmospheric stability, and exceeded the limit recommended by the WHO (150 μg m−3, 24-h) three times downwind from the GPP. Similarly, the mean SO2 concentrations at all three sites exceeded the limit established by the NOM-022-SSA1-2010 (288 μg m−3, 24-h), while NH3 concentrations exceeded the limits established by the OEHHA (100 μg m−3, 24-h) eight times at Nuevo Leon. A backward trajectory analysis indicated transport of air masses from the GPP to El Chimi and Estacion Delta sampling sites. The results indicate that GPP's emissions could affect the residents in the surrounding areas, warranting public health action to investigate exposures and risks.