Statistical assessment and modeling of the effects of weather conditions on H2S plume dispersal from Icelandic geothermal power plants

Episodes of high atmospheric load of hydrogen sulfide (H2S), where the concentration is over 50 μg m−3 hourly average value, occur about 80 times a year in Reykjavik (data from 2007 to 2009). H2S originates mainly from two geothermal power plants 25–30 km (south-)east of Reykjavik, at Hellisheidi and Nesjavellir. Certain weather-dependent dispersion conditions, such as wind, cloud cover and air temperature, allow the transport of emissions towards Reykjavik and the neighboring cities, causing local air pollution. High concentrations of H2S occur within a narrow range of weather conditions, namely slow (mean value 2 ± 1 m s−1) easterly (114° ± 23°) winds, together with cold air temperatures (median value −3 °C) and preferably no, or little, cloud cover. A classification of weather types shows the preferred occurrence of high H2S concentrations in connection with low atmospheric exchange and autochthonous weather. Stable atmospheric stratification and inversions enable the transport of H2S emissions to Reykjavik. The measured concentrations, the short lived peaks in concentration and different values at nearby measurement stations, indicate a very narrow plume, which fits well with a Gaussian plume distribution model.