Synoptic analysis of a decade of daily measurements of SO2 emission in the troposphere from volcanoes of the global ground-based Network for Observation of Volcanic and Atmospheric Change
Authors: Arellano Santiago , Galle Bo , Apaza Fredy , Avard Geoffroy , Barrington Charlotte , Bobrowski Nicole , Bucarey Claudia , Burbano Viviana , Burton Mike , Chacón Zoraida , Chigna Gustavo , Clarito Christian Joseph , Conde Vladimir , Costa Fidel , De Moor Maarten , Delgado-Granados Hugo , Di Muro Andrea , Fernandez Deborah , Garzón Gustavo , Gunawan Hendra , Haerani Nia , Hansteen Thor H. , Hidalgo Silvana , Inguaggiato Salvatore , Johansson Mattias , Kern Christoph , Kihlman Manne , Kowalski Philippe , Masias Pablo , Montalvo Francisco , Möller Joakim , Platt Ulrich , Rivera Claudia , Saballos Armando , Salerno Giuseppe , Taisne Benoit , Vásconez Freddy , Velásquez Gabriela , Vita Fabio , Yalire Mathieu 
Published: March 2021

Abstract. Volcanic plumes are common and far-reaching
manifestations of volcanic activity during and between eruptions.
Observations of the rate of emission and composition of volcanic plumes are
essential to recognize and, in some cases, predict the state of volcanic
activity. Measurements of the size and location of the plumes are important
to assess the impact of the emission from sporadic or localized events to
persistent or widespread processes of climatic and environmental importance.
These observations provide information on volatile budgets on Earth,
chemical evolution of magmas, and atmospheric circulation and dynamics.
Space-based observations during the last decades have given us a global view
of Earth's volcanic emission, particularly of sulfur dioxide (SO2).
Although none of the satellite missions were intended to be used for
measurement of volcanic gas emission, specially adapted algorithms have
produced time-averaged global emission budgets. These have confirmed that
tropospheric plumes, produced from persistent degassing of weak sources,
dominate the total emission of volcanic SO2. Although space-based
observations have provided this global insight into some aspects of Earth's
volcanism, it still has important limitations. The magnitude and short-term
variability of lower-atmosphere emissions, historically less accessible from
space, remain largely uncertain. Operational monitoring of volcanic plumes,
at scales relevant for adequate surveillance, has been facilitated through
the use of ground-based scanning differential optical absorption
spectrometer (ScanDOAS) instruments since the beginning of this century, largely due to
the coordinated effort of the Network for Observation of Volcanic and
Atmospheric Change (NOVAC). In this study, we present a compilation of
results of homogenized post-analysis of measurements of SO2 flux and
plume parameters obtained during the period March 2005 to January 2017 of 32
volcanoes in NOVAC. This inventory opens a window into the short-term
emission patterns of a diverse set of volcanoes in terms of magma
composition, geographical location, magnitude of emission, and style of
eruptive activity. We find that passive volcanic degassing is by no means a
stationary process in time and that large sub-daily variability is observed
in the flux of volcanic gases, which has implications for emission budgets
produced using short-term, sporadic observations. The use of a standard
evaluation method allows for intercomparison between different volcanoes and
between ground- and space-based measurements of the same volcanoes. The
emission of several weakly degassing volcanoes, undetected by satellites, is
presented for the first time. We also compare our results with those
reported in the literature, providing ranges of variability in emission not
accessible in the past. The open-access data repository introduced in this
article will enable further exploitation of this unique dataset, with a
focus on volcanological research, risk assessment, satellite-sensor
validation, and improved quantification of the prevalent tropospheric
component of global volcanic emission. Datasets for each volcano are made available at https://novac.chalmers.se (last access: 1 October 2020) under the CC-BY 4 license or through the DOI (digital
object identifier) links
provided in Table 1.