Implementation of electrochemical, optical and denuder-based sensors and sampling techniques on UAV for volcanic gas measurements: examples from Masaya, Turrialba and Stromboli volcanoes

Volcanoes are a natural source of several reactive
gases (e.g., sulfur and halogen containing species) and nonreactive
gases (e.g., carbon dioxide) to the atmosphere. The
relative abundance of carbon and sulfur in volcanic gas as
well as the total sulfur dioxide emission rate from a volcanic
vent are established parameters in current volcanomonitoring
strategies, and they oftentimes allow insights into
subsurface processes. However, chemical reactions involving
halogens are thought to have local to regional impact on
the atmospheric chemistry around passively degassing volcanoes.
In this study we demonstrate the successful deployment
of a multirotor UAV (quadcopter) system with custom-made
lightweight payloads for the compositional analysis and gas
flux estimation of volcanic plumes. The various applications
and their potential are presented and discussed in example
studies at three volcanoes encompassing flight heights of 450
to 3300m and various states of volcanic activity. Field applications
were performed at Stromboli volcano (Italy), Turrialba
volcano (Costa Rica) and Masaya volcano (Nicaragua).
Two in situ gas-measuring systems adapted for autonomous
airborne measurements, based on electrochemical and optical
detection principles, as well as an airborne sampling
unit, are introduced. We show volcanic gas composition results
including abundances of CO2, SO2 and halogen species.
The new instrumental setups were compared with established
instruments during ground-based measurements at Masaya
volcano, which resulted in CO2 = SO2 ratios of 3.6 0.4. For
total SO2 flux estimations a small differential optical absorption
spectroscopy (DOAS) system measured SO2 column
amounts on transversal flights below the plume at Turrialba
volcano, giving 1776 1108 T d􀀀1 and 1616 1007 T d􀀀1
of SO2 during two traverses. At Stromboli volcano, elevated
CO2 = SO2 ratios were observed at spatial and temporal proximity
to explosions by airborne in situ measurements. Reactive
bromine to sulfur ratios of 0.19 104 to 9.8 10􀀀4
were measured in situ in the plume of Stromboli volcano,
down wind of the vent.