Emission of gas and atmospheric dispersion of SO 2 during the December 2013 eruption at San Miguel volcano (El Salvador, Central America)

San Miguel volcano, El Salvador, erupted on 29 December 2013, after a 46 year period characterized by weak activity. Prior to the eruption a trend of increasing SO 2 emission rate was observed, with all values measured after mid‐November greater than the average value of the previous year (~310 t d −1 ). During the eruption, SO 2 emissions increased from the level of ~330 t d −1 to 2200 t d −1 , dropping after the eruption to an average level of 680 t d −1 . Wind measurements and SO 2 emission rates during the preeruptive, syneruptive, and posteruptive stages were used to model SO 2 dispersion around the volcano. Atmospheric SO 2 concentration exceeded the dangerous threshold of 5 ppm in the crater region and in some sectors with medium elevation of the highly visited volcanic cone. Combining the SO 2 emission rate with measured CO 2 /SO 2 , HCl/SO 2 , and HF/SO 2 plume gas ratios, we estimate the CO 2 , HCl, and HF outputs for the first time on this volcano.