Long-range transport of SO2 over South Africa: A case study of the Calbuco volcanic eruption in April 2015

Abstract

South Africa (SA) is influenced by anthropogenic SO2 emissions, however, no studies exist detailing the atmospheric or climatic effects resulting from volcanic eruptions at this location. In this work, the Calbuco volcano situated in southern Chile (41.79°S, 73.13°W), was used as a case study to investigate the transport of volcanic SO2 plumes over SA in 2015. The Calbuco volcano underwent a series of eruptive phases starting from 22 April 2015. In this study, HYSPLIT forward trajectories and cluster analysis were carried out in order to estimate the altitude level of air parcels entering the SA subcontinent. These analyses along with Ozone Monitoring Instrument (OMI) assessments confirmed that trajectories beginning in Calbuco arrived in SA during the last few days of April (∼28 April 2015) and stayed until the 1st week of May 2015 (∼2 May 2015). In order to estimate the rise in SO2 columnar concentrations at various altitudes and surface SO2 levels, OMI data and 19 ground-based (GB) monitoring stations (situated throughout SA) were utilized. A comparative analysis employing SO2 data from pre-2014 and post-2016 volcanic eruption periods were also included in this study. Results showed that a major increase in SO2 concentration was observed at the Planetary Boundary Layer (∼ 2 DU) when compared to its upper layers during April and May 2015. Although some GB stations in North West province namely Damonsville, Mmabatho and Phola showed a moderate increase in SO2 values during April and May 2015, there was no significant rise in GB measurements at the surface in other locations However, we are not certain due to data gaps in the measurements and non-availability of ground-based measurements.