Fig. 3. Volcanic molar gas composition.

CO₂-SO₂ and H₂O-SO₂ regression scatterplots for (A and B) 30 October 2018 21:00 UTC (07:00 local time), (C and D) flight 1 on 22 May 2019 06:30 UTC (16:30 local time), (E and F) flight 2 on 23 May 2019 00:00 UTC (10:00 local time), and (G) flight 4 on 26 May 2019 00:00 UTC (10:00 local time). CO₂ is shown as “excess,” where the background is taken as the y-axis intercept of the regression line. There is high variability in CO₂ at low SO₂ (dilute plume) conditions. Molar gas ratios are determined by least squares linear regression (solid blue line). Goodness of fit is shown by the adjusted r² values. Gray shaded region represents the 95% confidence bounds on the regression. Data are from two Multi-GAS instruments: (A to F) Università di Palermo and (G) Chalmers University (see Materials and Methods for specifications).