Erratum to: Measurements of volcanic SO 2 and CO 2 fluxes by combined DOAS, Multi-GAS and FTIR observations: a case study from Turrialba and Telica volcanoes

Over the past few decades, substantial progress has been made to overcome the technical difficulties of continuously measuring volcanic SO 2 emissions. However, measurements of CO 2 emissions still present many difficulties, partly due to the lack of instruments that can directly measure CO 2 emissions and partly due to its strong atmospheric background. In order to overcome these difficulties, a commonly taken approach is to combine differential optical absorption spectroscopy (DOAS) by using NOVAC scan-DOAS instruments for continuous measurements of crateric SO 2 emissions, and electrochemical/NDIR multi-component gas analyser system (multi-GAS) instruments for measuring CO 2 /SO 2 ratios of excerpts of the volcanic plume. This study aims to quantify the representativeness of excerpts of CO 2 /SO 2 ratios measured by Multi-GAS as a fraction of the whole plume composition, by comparison with simultaneously measured CO 2 /SO 2 ratios using cross-crater Fourier transform infrared spectroscopy (FTIR). Two study cases are presented: Telica volcano (Nicaragua), with a homogenous plume, quiescent degassing from a deep source and ambient temperature, and Turrialba volcano (Costa Rica), which has a non-homogeneous plume from three main sources with different compositions and temperatures. Our comparison shows that in our “easier case” (Telica), FTIR and Multi-GAS CO 2 /SO 2 ratios agree within a factor about 3 %. In our “complicated case” (Turrialba), Multi-GAS and FTIR yield CO 2 /SO 2 ratios differing by approximately 13–25 % at most. These results suggest that a fair estimation of volcanic CO 2 emissions can be provided by the combination of DOAS and Multi-GAS instruments for volcanoes with similar degassing conditions as Telica or Turrialba. Based on the results of this comparison, we report that by the time our measurements were made, Telica and Turrialba were emitting approximately 100 and 1,000 t day −1 of CO 2 , respectively.