Volcanic CO2 emission rate data are sparse despite their potential importance for constraining the role of magma degassing in the biogeochemical 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 Popocate??petl volcano on June 7 and 10, 1995. LI-COR sample paths of ???72 m, compared with ???1 km for the analyzer customarily used, together with fast Fourier transforms to remove instrument noise from raw data greatly improve resolution of volcanic CO2 anomalies. Parametric models fit to background CO2 provide a statistical tool for distinguishing volcanic from ambient CO2. Global Positioning System referenced flight traverses provide vastly improved data on the shape, coherence, and spatial distribution of volcanic CO2 in plume cross sections and contrast markedly with previous results based on traverse stacking. The continuous escape of CO2 and SO2 from Popocate??petl was fundamentally noneruptive and represented quiescent magma degassing from the top of a magma chamber ???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 -9000 t d-1. Analysis of random errors indicates emission rates have 95% confidence intervals of ?????20%, with uncertainty contributed mostly by wind speed variance, although the variance of plume cross-sectional areas during traversing is poorly constrained and possibly significant. Copyright 1997 by the American Geophysical Union.
Additional Publication Details
Application of the LI-COR CO2 analyzer to volcanic plumes: A case study, volcan Popocate??petl, Mexico, June 7 and 10, 1995