Fig. 6. Carbon isotope composition of Manam volcanic gas plume.

(A) Isotopic composition and CO₂ concentration of samples collected by UAS in the plume emanating from the Southern Crater (black circles) and in clean ocean air (orange circle), extrapolated to 100% CO₂ by least squares linear regression (blue line). The gray shaded region shows the 95% confidence bounds on the regression. Uncertainties on the measurements are smaller than the symbol size unless shown. (B) The timing of bag sampling (“pump-activated”) shown relative to SO₂ concentrations measured by co-located Multi-GAS instrument on 26 May 2019. Only the second pump activation was triggered within dense plume conditions (>5 ppm SO₂). (C) Sampling apparatus mounted on the multirotor UAS, comprising four Tedlar bags connected in series with the Multi-GAS and its pump. Image credit: T. Fischer.