Emission of gas and atmospheric dispersion of SO2 during the December 2013 eruption at San Miguel volcano (El Salvador, Central America).

Abstract 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 SO2 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, SO2 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 SO2 emission rates during the preeruptive,
syneruptive, and posteruptive stages were used to model SO2 dispersion around the volcano. Atmospheric
SO2 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 SO2 emission rate with measured
CO2/SO2, HCl/SO2, and HF/SO2 plume gas ratios, we estimate the CO2, HCl, and HF outputs for the first time
on this volcano.