Estimate of carbonyl sulfide (OCS) volcanic source strength deduced from OCS/CO2 ratios in volcanic gases

Measurements of the concentration ratio of OCS and CO2 were made in fumaroles of several volcanoes in Italy and Nicaragua. The values obtained, together with previous published data, demonstrate that the OCS/CO2 ratio is positively correlated with the emission temperature of the gases. It ranges from 10 −7.1 to 10 −2.7 at the Vulcano (90°C) and Erta'Ale (1130°C) volcanoes, respectively. The global OCS volcanic source strength, deduced from SO2 emission rates, CO2/SO2 and OCS/CO2 ratios in volcanic gases, is estimated to be in the range 6‐90 ×10 9 gOCS per year.