APPLICATION OF THE LI-COR CO2 ANALYZER TO VOLCANIC PLUMES - A CASE-STUDY, VOLCAN-POPOCATEPETL, MEXICO, JUNE 7-10, 1995

Volcanic CO2 emission rate data are sparse despite their potential imp ortance for constraining the role of magma degassing in the biogeochem ical cycle of carbon and for assessing volcanic hazards. We used a LI- COR CO2 analyzer to determine volcanic CO2 emission rates by airborne measurements in volcanic plumes at Popocatepetl volcano on June 7 and 10, 1995. LI-COR sample, paths of similar to 72 m, compared with simil ar to 1 km for the analyzer customarily used, together with fast Fouri er transforms to remove instrument noise from raw data greatly improve resolution of volcanic CO2 anomalies. Parametric models fit to backgr ound CO2 provide a statistical tool for distinguishing volcanic from a mbient CO2. Global Positioning System referenced flight traverses prov ide vastly improved data on the shape, coherence, and spatial distribu tion of volcanic CO2 in plume cross sections and contrast markedly wit h previous results based on traverse stacking. The continuous escape o f CO2 and SO2 from Popocatepetl was fundamentally noneruptive and repr esented quiescent magma degassing from the top of a magma chamber simi lar to 5 km deep. The average CO2 emission rate for January-June 1995 is estimated to be at least 6400 t d(-1) one of the highest determined for a quiescently degassing volcano, although correction for downwind dispersion effects on volcanic CO2 indicates a higher rate of similar to 9000 t d(-1). Analysis of random errors indicates emission rates h ave 95% confidence intervals of similar to+/-20%, with uncertainty con tributed mostly by wind speed variance, although the variance of plume cross-sectional areas during traversing is poorly constrained and pos sibly significant.