COMPARISONS BETWEEN OMI SO2 DATA AND GROUND-BASED SO2 MEASUREMENTS AT TURRIALBA VOLCANO

Turrialba is one of the largest and most active stratovolcanoes in the Central Cordillera of Costa Rica with an elevation of 3340 m a.s.l. Located just 35 km northeast of the capital city of San Jose and even closer to other densely populated areas, this volcano poses a threat to the country’s economic interests and aviation due to its recorded eruptive history, the surrounding steep slopes and valleys, and the regional meteorological conditions. It has been constantly degassing SO₂ for several years with a significant increase in 2007 that has been attributed to a shallow magmatic intrusion, and renewed its eruptive activity during a series of short phreatic explosions on January 5-6, 2010 which resulted in ashfall in San Jose. Gas emissions from Turrialba volcano could have potentially significant impacts on human health, the surrounding vegetation and ecosystems, and regional climate, but information on validated SO₂ mass and fluxes from the volcano are scarce. Such data are needed to monitor the changes in volcanic activity that may serve as eruption precursors and to further understand the magnitude and the extent of the effects on the environment.

We have collated the available ground-based SO₂ flux data collected at Turrialba volcano, from infrequent deployments of scanning miniaturized differential optical absorption spectroscopy (Mini DOAS) instruments, published and unpublished reports from 2010-2011, the NOVAC project database, and from personal field campaigns during July 2010 and January 2011. These data are compared to SO₂ measurements made by the Ozone Monitoring Instrument (OMI) onboard the Aura satellite during the same period to attempt validation of the satellite data and to assess the utility of the satellite measurements for monitoring degassing at Turrialba. We also compare the ground-based data with results from automated OMI data processing using the Band Residual Difference algorithm and a manual procedure similar to the Normalized Cloud-mass technique, to evaluate the relative accuracy of automatic and non-automatic OMI analysis procedures. This will permit improvements in data processing techniques for operational use (e.g., quantification of SO₂ emissions in near real-time).