Implementation of electrochemical, optical and denuder-based sensors and sampling techniques on UAV for volcanic gas measurements: examples from Masaya, Turrialba and Stromboli volcanoes
Abstract. 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 volcano-monitoring
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
3300 m 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 CO 2 ,
SO 2 and halogen species. The new instrumental setups were compared with
established instruments during ground-based measurements at Masaya volcano,
which resulted in CO 2 ∕  SO 2 ratios of 3.6  ±  0.4. For
total SO 2 flux estimations a small differential optical absorption
spectroscopy (DOAS) system measured SO 2 column amounts on transversal
flights below the plume at Turrialba volcano, giving
1776  ±  1108 T d −1 and 1616  ±  1007 T d −1 of SO 2 
during two traverses. At Stromboli volcano, elevated CO 2 ∕  SO 2 
ratios were observed at spatial and temporal proximity to explosions by
airborne in situ measurements. Reactive bromine to sulfur ratios of
0.19  ×  10 −4 to 9.8  ×  10 −4 were measured in situ
in the plume of Stromboli volcano, downwind of the vent.