03 Mar 2022
03 Mar 2022
Status: this preprint is currently under review for the journal AMT.

Development and Testing of a Novel Sulfur Dioxide Sonde

Subin Yoon1, Alexander Kotsakis1,a, Sergio L. Alvarez1, Mark G. Spychala2,b, Elizabeth Klovenski1, Paul Walter2, Gary Morris2,c, Ernesto Corrales3, Alfredo Alan3, Jorge A. Diaz3,d, and James H. Flynn1 Subin Yoon et al.
  • 1Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, 77004, USA
  • 2St. Edward’s University, Austin, TX, 78704, USA
  • 3GasLAB, CICANUM. Universidad de Costa Rica, San José, Costa Rica
  • anow at: ERT, Inc., Laurel, MD, 20707, USA
  • bnow at: Hamelmann Communications, Pagosa Springs, CO, 81147, USA
  • cnow at: NOAA Global Monitoring Laboratory, Boulder, CO, 80305, USA
  • dnow at: INFICON, East Syracuse, NY, 13057, United States

Abstract. A novel technique has been developed to measure sulfur dioxide (SO2) using a modification of the existing electrochemical concentration cell (ECC) ozonesonde technology. The current sonde-based method to measure SO2 (i.e. the dual-sonde approach) involves launching two ozonesondes together with one of the sondes having a filter to remove SO2 at the inlet. The SO2 profile is determined by taking the difference between the measurements from the two instruments. The dual-sonde method works well in typical tropospheric conditions when [O3] > [SO2] but saturates when [SO2] > [O3] and has large uncertainties in the upper troposphere/lower stratosphere that would limit its effectiveness in measuring SO2 from an explosive volcanic eruption. Due to these 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 O3 removal filter, and (3) the addition of a sample dryer. The SO2 sonde measures SO2 as a reduction in the cell current. There was a strong correlation (r2 > 0.94) between the SO2 sonde and a Thermo 43c analyzer during controlled laboratory tests and pre-flight tests. Varying humidity levels affected the SO2 sonde’s sensitivity (84.6 ± 31.7 ppbv/µA, 1σ = 37 %) during initial field tests, which was resolved by adding a sample dryer upstream of the O3 removal filter and pump inlet. This modification significantly reduced the variability and increased the sensitivity of the SO2 measurements (47 ± 5.8 ppbv/µA, 1σ = 12 %). Field tests included measurements near Kīlauea Volcano (before and during the 2018 eruption of the Lower East Rift Zone), Costa Rica’s Turrialba Volcano, and anthropogenic plumes from the Athabasca Oil Sands region of Alberta, Canada. This single SO2 sonde system is an effective, inexpensive instrument for measuring both ground-based and vertical profiles of SO2 from anthropogenic and natural sources (i.e. volcanic eruptions) over a wide range of concentrations.

Subin Yoon et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-66', Anonymous Referee #1, 29 Mar 2022
    • AC1: 'Reply on RC1', Subin Yoon, 24 May 2022
  • RC2: 'Comment on amt-2022-66', Anonymous Referee #2, 22 Apr 2022
    • AC2: 'Reply on RC2', Subin Yoon, 24 May 2022

Subin Yoon et al.

Subin Yoon et al.


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Short summary
SO2 is adverse to human health and the environment. A single SO2 sonde was developed to provide direct SO2 measurement with a greater vertical extent, a lower limit of detection, and less uncertainty relative to the previous dual sonde method. The single sonde was tested in the field near volcanos and anthropogenic sources where the sonde measured SO2 ranging from 0.5 to 940 ppb. This lighter weight payload can be a great candidate to attach to small drones and unmanned aerial vehicles.