SO2 flux and gas composition from the Pacaya 2021 eruption

This is the supporting data of the paper " "Gas measurements reveal fractional degassing and water interaction during a flank eruption of Pacaya Volcano (Guatemala)." There are three types of data: SO2 fluxes measured with Tropomi images. SO2 fluxes using a ground-based UV SO2 camera, and the raw Multigas measurements. Tropomi The TropomiProcessed folder contains the SO2 and cloud maps obtained from the Tropomi images, and the SO2 flux calculated, as a function of distance downwind from the volcano, by processing these images using the traverse method (Bluth et al., 2008), adapted for the resolution and a-priori altitude profiles of the Tropomi SO2 products (Theys et al., 2019). The plume altitude was assumed as 3000 m a.s.l. for most of the days and 2500 when the wind was stronger than 12 m/s, based on our observations of the plume behavior. The SO2 Vertical Column Density (VCD) was interpolated at plume height between the VCDs at 1km and at 7km provided in the net-cdf file. and the wind data needed to calculate the flux are produced by the Global Data Assimilation System, which are available at the portal of the National Ocean and Atmosphere Administration (https://www.ready.noaa.gov/READYamet.php). The limitations of this method occur when high and thick clouds mask the SO2 absorption signal of the plume, and when the wind field is too weak to produce a suitable dispersion pattern of the plume. The former case is identified by looking at the cloud fraction and cloud pressure metadata of Tropomi file, while the latter case is identifiable through a visual analysis of the plume shape on the SO2 map. SO2 Camera The UVcamera folder contains the data from the SO2 camera measurements on 15/01/2016, 16/01/2016, 22/06/2018, and 30/03/2021. The data is organized as subfolders containing sequences of continuous data. Each subfolder contains the raw data of the camera (pairs of 16-bits binary image files and a text file, named after their acquisition time), images used to correct and dark currents and vigneting, Jpeg distribution mats of the SO2 in the plume, and a text, or excel file containing the temporal evolution of SO2 flux calculated on each image of the sequence. For each day, a folder also contains JPEG monochrome previsualization images from each camera. The ground based SO2 flux were measured with an SO2 camera during three campaigns, in January 2016 and June 2018, during normal, mild strombolian activity in the McKenney crater, and in April 2021 during a phase of abundant lava effusion from a radial fissure. The instrument consists of two Alta U260 cameras equipped with Asahi 310 and 330 bandpass filters collocated in front of the lenses (Pentax BUV2528 or Universe Kogaku B1228 depending on the distance to the plume). The image pairs were processed with the methodology described in Campion et al. (2015) which includes a calibration with SO2-filled quartz cells (with Column Densities of 0, 1005, 1540 and 4580 ppm) and a correction of the light dilution effect. In favorable conditions (i.e. no clouds in the Field of View, ash-free plume, SO2 CD <4000 ppm, distance < 5km) this methodology gives results with an accuracy of +/- 25%, with the plume-to-instrument distance dominating the error budget. Its detection limit at a distance of 5km is 120 ppm.m which, with a wind of 10 m/s, results into an SO2 flux detection limit of 0.5 kg/s. Multigas The MultigasData folder contains Excel files of multigas measurement from each measurement point. The Excel files contain the raw data (in mA) from the sensors, the pressure temperature and relative humidity, the calibrated concentrations of CO2, H2O, SO2 and H2S, and correlation plots between the different gas concentrations between them, after the appropriate correction of the instrumental response slowness has been done. We utilized a Multigas system to measure time series of CO2, SO2, H2S, and H2O concentrations (Shinohara, 2005), comprising an infrared spectrometer (GASCARD NG sensor from Edinburgh Instruments for CO2, range 0-1000 ppm), and two electrochemical sensors (T3TH for SO2, range 0-50 ppm; T3H for H2S, range 0-20 ppm). The gas was pumped at a constant flow rate (0.5 l/min) through a silicone tube and circulated successively in the sensor array. The 4-20 mA data from every sensors were collected and stored in an MSR data logger (model 145) that also measured pressure, temperature and relative humidity. The H2O molar mixing ratio (in ppm) is calculated from the relative humidity, pressure and temperature measurements using the Goff-Gratch (1946) equation. This Multigas was calibrated in Mexico-City at pressure and temperature similar to those prevailing in Pacaya (~750 hPa and 15-20°C). The Multigas measures time series of gas concentrations that are correlated with each other. The concentration ratio is calculated as the slope of the linear regression between the gas concentration time series, after correcting for the instrumental delay between them, and applying a numerical filter to take into account the temporal response of the sensors. In data processing, efforts were made to obtain coefficients exhibiting the highest R-squared values to achieve the best results.