NOVAC scanning DOAS spectral data and derived sulfur dioxide emission rates for Mount Cleveland, Alaska

The Network for Observation of Volcanic and Atmospheric Change (NOVAC) is a community of volcano observatories and research institutions that together develop and apply ultraviolet differential optical absorption spectroscopy (DOAS) instruments to measure volcanic gas emission rates. The collected data are used for assessment of volcanic activity, eruption forecasting, research on volcanic processes, and studying the atmospheric impact of volcanic degassing. Together, the institutions participating in NOVAC run the largest instrument network for monitoring gas emissions from volcanoes around the world (Galle et al., 2010; Arellano et al., 2021).

In 2022 and 2023, the Alaska Volcano Observatory (AVO) installed two NOVAC scanning DOAS instruments on Mount Cleveland, an actively degassing volcano in Alaska. Instrument MAYP115019 was installed at site CLNE (52.84 N, -169.92 E, 325 m above sea level) on the northeast flank of the volcanic edifice on 13 September 2022. Instrument MAYP115415 was installed at site CLES (52.82 N, -169.90 E, 150 m above sea level) on the volcano’s east side on 16 May 2023. Both instruments are approximately 3 km from the volcano’s summit. During daytime hours, they scan the sky from horizon to horizon and collect scattered solar radiation in a 60 deg cone around the volcano (Galle et al., 2010). The collected light is coupled into fiber optic cables and transmitted to spectrometers installed within the station enclosures. The instruments measure the skylight spectrum in the ultraviolet range between 280 and 380 nm and store the recorded spectra on site. Horizon-to-horizon measurements (i.e., one scan) typically take between 5 and 15 minutes to complete, depending on the sunlight intensity, which varies with time of day and season. Typically, about 70 scans are acquired each day. At regular intervals, the spectral data are telemetered via radio link and the internet to AVO. Technical issues interrupt instrument operation at various times, and some data gaps exist. Figure1.jpg shows a photograph of AVO field engineers working at CLES. Aimed at the volcano’s summit, the black DOAS scanner is mounted on the tallest mast at the site.

Spectral data arriving at AVO are evaluated using conventional DOAS analysis routines (Platt and Stutz, 2008). The spectra are examined for the presence of characteristic absorption features caused by sulfur dioxide (SO2) along the instrument line of sight. Integration along a full scan allows derivation of the cross-sectional SO2 burden in overhead volcanic plumes which, when multiplied by the wind speed (Hersbach et al., 2023), allows derivation of the SO2 emission rate (Kushner, 2023; Kern, 2025). The emission rate describes the amount of SO2 emitting from the volcano, e.g., in metric tons per day (t/d) or kilograms per second (kg/s). On first order, the SO2 emission rate is linked to the amount of magma arriving at shallow depths (about 3 km or shallower at Mount Cleveland; Werner et al., 2020) where sulfur partitions from the silicate melt into a separate fluid phase that can escape to the surface where it is emitted as SO2.

This data release contains two types of data: Cleveland_SpectralRadiance.zip contains the raw spectral radiance measured by the spectrometers. The archive contains numerous *.pak files, each corresponding to a full scan of the sky. The *.pak files can be extracted using the free NOVAC Program (download links available at https://novac-community.org/software).

Cleveland_SO2_EmissionRate.csv provides a table containing the results of an automated DOAS analysis of the spectral data performed using the NOVAC Program. Among other parameters, this table lists a time series of SO2 emission rates which will be of most interest to most users. A detailed description of the spectral data and all parameters listed in the table are provided in the attached metadata.

The NOVAC scanning DOAS instruments at Mount Cleveland continue to be operated by the AVO and are acquiring new data. The initial data release contains data collected between 19 October 2022 (the start of the measurements) and 31 May 2026. This data release will be updated at regular intervals to include additional data.

References

Arellano, S., Galle, B., Apaza, F., Avard, G., Barrington, C., Bobrowski, N., Bucarey, C., Burbano, V., Burton, M., Chacón, Z., Chigna, G., Clarito, C.J., Conde, V., Costa, F., de Moor, M., Delgado-Granados, H., di Muro, A., Fernandez, D., Garzón, G., Gunawan, H., Haerani, N., Hansteen, T., Hidalgo, S., Inguaggiato, S., Johansson, M., Kern, C., Kihlman, M., Kowalski, P., Masias, P., Montalvo, F., Möller, J., Platt, U., Rivera, C., Saballos, A., Salerno, G., Taisne, B., Vásconez, F., Velásquez, G., Vita, F., Yalire, M., 2021. Synoptic Analysis of a Decade of Daily Measurements of SO2 Emission in the Troposphere from Volcanoes of the Global Ground-Based Network for Observation of Volcanic and Atmospheric Change. Earth Syst Sci Data 13, 1167–1188. https://doi.org/10.5194/essd-13-1167-2021

Galle, B., Johansson, M., Rivera, C., Zhang, Y., Kihlman, M., Kern, C., Lehmann, T., Platt, U., Arellano, S., Hidalgo, S., 2010. Network for Observation of Volcanic and Atmospheric Change (NOVAC)—A global network for volcanic gas monitoring: Network layout and instrument description. J Geophys Res 115, D05304. https://doi.org/10.1029/2009JD011823

Hersbach, H., Bell, B., Berrisford, P., Biavati, G., Horányi, A., Muñoz Sabater, J., Nicolas, J., Peubey, C., Radu, R., Rozum, I., Schepers, D., Simmons, A., Soci, C., Dee, D., Thépaut, J-N. (2023): ERA5 hourly data on pressure levels from 1940 to present. Copernicus Climate Change Service (C3S) Climate Data Store (CDS), DOI: 10.24381/cds.bd0915c6 (Accessed on 17 June 2026)

Kern, C., 2025. Ultraviolet and visible remote sensing of volcanic gas emissions. Journal of Volcanology and Geothermal Research 468, 108423. https://doi.org/10.1016/j.jvolgeores.2025.108423

Kushner, D.S. (2023). Volcanic gas quantification under suboptimal conditions. Dissertation, University of Alaska Fairbanks. https://scholarworks.alaska.edu/uaf_grad_geosci/311

Platt, U., Stutz, J., 2008. Differential Optical Absorption Spectroscopy - Principles and Applications. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-75776-4

Werner, C., Rasmussen, D.J., Plank, T., Kelly, P.J., Kern, C., Lopez, T., Gliss, J., Power, J.A., Roman, D.C., Izbekov, P., Lyons, J., 2020. Linking Subsurface to Surface Using Gas Emission and Melt Inclusion Data at Mount Cleveland Volcano, Alaska. Geochemistry, Geophysics, Geosystems 21, 1–33. https://doi.org/10.1029/2019GC008882