Sensitivity tests for improved retrievals of SO2 plume height from TROPOMI observations
- 1Royal Belgian Institute for Space Aeronomy (BIRA-IASB), D31 UV-Visible observations, Belgium (lorenzo.fabris@aeronomie.be)
- 2Université libre de Bruxelles (ULB)
Sulfur dioxide (SO2), emitted from volcanic eruptions, can have a major impact on the environment and society. While nadir-viewing satellites have been providing precise information on its Vertical Column Density (VCD) for several decades, the retrieval of its Layer Height (LH) is a more recent development, although it is important for the aviation safety, estimation of SO2 emissions, understanding of volcanic processes and climate research. In the Ultraviolet (UV), the current algorithms are often time-consuming and still lack sensitivity, especially in the presence of aerosols.
Our research aims at developing an improved SO2 LH (and VCD) retrieval algorithm for the TROPOspheric Monitoring Instrument (TROPOMI). While the third spectral band of TROPOMI is traditionally used for sulfur dioxide, a shorter UV region has been exploited here to take advantage of the strong absorption of SO2 in the second band. As a demonstration case, Slant Column Density (SCD) retrievals in band 2 were carried out using the Covariance-Based Retrieval Algorithm (COBRA) [1]. We show that SO2 SCDs from both spectral bands are generally in excellent agreement. However, the results in band 2 reveal a greater sensitivity to SO2 than in band 3.
Motivated by this result, we performed SO2 plume height retrievals on an extensive set of synthetic spectra representative of TROPOMI observation conditions, using the Look-Up Tables Covariance-Based Retrieval Algorithm (LUT-COBRA) [2]. The SO2 LHs and VCDs we find from the second band are more accurate, and the associated retrieval errors appear to be considerably reduced in comparison to those of the band 3.
In addition, sensitivity analyses were conducted to further characterise the wavelength dependence and effect of some observation conditions on the quality of these retrievals. More specifically, we assess the impact of the temperature, air density, ozone profile and VCD, SO2 absorption cross sections, surface albedo and height as well as the SO2 profile shape.
Finally, we present the next steps to further develop the LUT-COBRA approach and application to TROPOMI band 2 measurements.
[1] N. Theys et al. Atmospheric Chemistry and Physics, 21(22):16727–16744, 2021.
[2] N. Theys et al. Atmospheric Measurement Techniques, 15(16):4801–4817, 2022.
How to cite: Fabris, L., Theys, N., Clarisse, L., Brenot, H., Yu, H., van Gent, J., Vlietinck, J., and Van Roozendael, M.: Sensitivity tests for improved retrievals of SO2 plume height from TROPOMI observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8314, https://doi.org/10.5194/egusphere-egu24-8314, 2024.
