PDF Version

Balloon-based SO2 Measurements during the Hunga Tonga Eruption

P. Walter1, J.H. Flynn2, S.L. Alvarez2, J. Brioude3,4, S. Evan5, J. Metzger6, G.A. Morris1, S. Yoon2, A. Kotsakis7,8, E. Klovenski2, M.D. Spychala9,1, E. Corrales10, A. Alan10, J.A. Diaz11,12 and J. Harnetiaux13

1St. Edward's University, Austin, TX 78704; 512-364-3158, E-mail: pauljw@stedwards.edu
2University of Houston, Houston, TX 77004
3Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309
4NOAA Chemical Sciences Laboratory (CSL), Boulder, CO 80305
5Laboratoire de l’Atmosphère et Cyclones LACy / UMR8105, Université de La Réunion, 97744 Saint-Denis Cedex 09, France
6Observatoire des Sciences de l’Univers OSU-Réunion / UMS3365, Université de La Réunion, CNRS, France
7ERT, Inc., Laurel, MD 20707
8Formerly University of Houston, Houston, TX 77004
9New Mexico State University, Las Cruces, NM 88003
10Universidad de Costa Rica, San Jose, Costa Rica
11INFICON, East Syracuse, NY 13057
12Formerly Universidad de Costa Rica, San Jose, Costa Rica
13En-Sci, Westminster, CO 80234

A novel technique has been developed to measure sulfur dioxide (SO2) using a modification of the existing electrochemical concentration cell (ECC) ozonesonde technology. The previous sonde-based method to measure SO2 (i.e. the dual-sonde approach) has large uncertainties in the stratosphere that would limit its effectiveness in measuring SO2 from an explosive volcanic eruption. Due to that and other limitations, several modifications were made to create a single-sonde system that would directly measure SO2 (i.e. the SO2 sonde). These modifications included (1) a positively biased ECC background current, (2) the addition of an ozone (O3) removal filter, and (3) the addition of a sample dryer. The SO2 sonde measures SO2 as a reduction in the cell current. Field tests in 2018 included lower tropospheric measurements near Kīlauea Volcano (before and during the 2018 eruption in the Lower East Rift Zone), Costa Rica’s Turrialba Volcano, and anthropogenic plumes from the Athabasca Oil Sands region of Alberta, Canada. The SO2 sonde was deployed to La Réunion as part of the Tonga volcano Rapid Response Experiment (TR2Ex).  During 21-25 January 2022, the SO2 sonde sampled SO2 in the stratospheric Hunga Tonga volcanic plume during four free-release balloon flights. Two of those soundings also had ozonesondes, and notches in the ozone data were observed in the plume. The altitudes of those plumes ranged from 19 to 30 km. We will overview the SO2 sonde measurements during the initial TR2Ex deployment and compare the SO2 sonde and ozonesonde measurements.

Figure 1

Figure 1. Vertical profile of SO2 from a measurement taken using an SO2 sonde on 21 January 2022 from the Maïdo Observatory in La Réunion.