Comparison of operational satellite SO₂ products with ground-based observations in northern Finland during the Icelandic Holuhraun fissure eruption

• Main Authors: I. Ialongo, J. Hakkarainen, R. Kivi, P. Anttila, N. A. Krotkov, K. Yang, C. Li, S. Tukiainen, S. Hassinen, J. Tamminen
• Format: Article
• Language: English
• Published: Copernicus Publications 2015-06-01
• Series: Atmospheric Measurement Techniques
• Online Access: http://www.atmos-meas-tech.net/8/2279/2015/amt-8-2279-2015.pdf
• ISSN: 1867-1381; 1867-8548

This paper shows the results of the comparison of satellite SO₂ observations from OMI (Ozone Monitoring Instrument) and OMPS (Ozone Mapping Profiler Suite) with ground-based measurements during the Icelandic Holuhraun fissure eruption in September 2014. The volcanic plume reached Finland on several days during the month of September. The SO₂ total columns from the Brewer direct sun (DS) measurements in Sodankylä (67.42° N, 26.59° E), northern Finland, are compared to the satellite data. <br><br> The operational satellite SO₂ products are evaluated for high latitude conditions (e.g. large solar zenith angle, SZA). The results show that the best agreement can be found for lowest SZAs, close-to-nadir satellite pixels, cloud fraction below 0.3 and small distance between the station and the centre of the pixel. Under good retrieval conditions, the difference between satellite data and Brewer measurements remains mostly below the uncertainty on the satellite SO₂ retrievals (up to about 2 DU at high latitudes). <br><br> The satellite products assuming a priori profile with SO₂ predominantly in the planetary boundary layer give total column values with the best agreement with the ground-based data. <br><br> The analysis of the SO₂ surface concentrations at four air quality stations in northern Finland shows that the volcanic plume coming from Iceland was located very close to the surface. This is connected to the fact that this was a fissure eruption and most of the SO₂ was emitted into the troposphere. This is an exceptional case because the SO₂ volcanic emissions directly affect the air quality levels at surface in an otherwise pristine environment like northern Finland. The time evolution of the SO₂ concentrations peaks during the same days when large SO₂ total column values are measured by the Brewer in Sodankylä and enhanced SO₂ signal is visible over northern Finland from the satellite maps. Thus, the satellite retrievals were able to detect the spatiotemporal evolution of the volcanic plume as compared to the surface observations. <br><br> Furthermore, direct-broadcast SO₂ satellite data (from both OMI and OMPS instruments) are compared for the first time against ground-based observations.