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: November 2020

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 sulphur 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 spectrometers (ScanDOAS) 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 on 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 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-sensors validation, and improved quantification of the prevalent tropospheric component of global volcanic emission. Data sets for each volcano are made available at https://novac.chalmers.se, under license CC-BY 4, or through the DOI-links provided in Table 1.