Supplementary Material for: Measuring the electrical charge and settling velocity of volcanic ash particles with a new, cost-effective apparatus (VoltAsh) both in the laboratory and in the field

Supplementary material for: Measuring the electrical charge and settling velocity of volcanic ash particles Allan Fries*1, Eduardo Rossi1, Jonathan P. Merrison2, Jens Jacob Iversen2, Tatsushi Matsuyama3, Frédéric Arlaud1, Jonathan Lemus1,4, Simon Thivet1, Carolina Diaz-Vecino1, Riccardo Simionato1,4, Costanza Bonadonna1 1 Département des Sciences de la Terre, University of Geneva 2 Department of Physics and Astronomy, Aarhus University 3 Department of Science and Engineering for Sustainable Innovation, Soka University 4 Département d’informatique, University of Geneva * [email protected] [corresponding author] ORCiD (AF): 0000.0002.9060.1357 ORCiD (ER): 0000.0003.3749.5804 ORCiD (JPM): 0000.0003.4362.6356 ORCiD (JJI): 0000.0002.7879.6163 ORCiD (TM): 0000.000272719212 ORCiD (JL): 0009.0001.3644.0126 ORCiD (ST): 0000.0003.0836.6421 ORCiD (CDV): 0009.0002.4084.6484 ORCiD (RS): 0000.0002.1283.3136 ORCiD (CB): 0000.0002.2368.2193 TABLE OF CONTENT: Supplementary Figures • Figure S1: 3D view of the printed circuit board with the embedded charge amplifier. • Figure S2: Schematic circuit diagram of the bipolar to unipolar converter. • Figure S3: TTFCs used in field and laboratory experiments. • Figure S4: Schematic view of the charge amplifier, bipolar to unipolar converter and connections with the Arduino board for the autonomous version. • Figure S5: Celestron handheld digital microscope images of the particles used in laboratory experiments A. E1-E12, B. E14 and E18, C. E16, D. and E13 and E17. • Figure S6: Surface charge densities and charge to mass ratios for particles in laboratory experiments. • Figure S7: Surface charge densities and charge to mass ratios for all the particles detected during field experiments at Sakurajima and Etna volcanoes. • Figure S8: Raspberry Pi version of VoltAsh. • Figure S9: Atmospheric parameters associated with analysed eruptions. • Figure S10: Grainsize distribution of the sample collected in a tray at location E2. Supplementary Tables • Table S1: GPS coordinates of the field locations • Table S2: List of samples collected on adhesive tape. • Table S3: Schematic view of the charge amplifier, bipolar to unipolar converter and connections with the Arduino board for the autonomous version. Supplementary Data • Data S1: Sketch for continuous voltage measurements and data save. • Data S2: Laboratory experiments: description of the different tests, high speed videos; voltage signals associated with the experiments. • Data S3: Field experiments: voltage signals recorded during field experiments. • DataS4: Measurements of the particle charge and velocity at Sakurajima volcano. • DataS5: Measurements of the particle charge and velocity at Etna volcano. Figure S1 – 3D view of the printed circuit board with the embedded charge amplifier. [A] Top view. [B] Bottom view. Figure S2 – Schematic circuit diagram of the bipolar to unipolar converter used in the autonomous version of the instrument. Figure S3 – TTFCs used in field and laboratory experiments, with corresponding aperture diameter D and lengths L given below in mm. Figure S4 –Schematic view of the charge amplifier, bipolar to unipolar converter and connections with the Arduino board for the autonomous version. Figure S5 – Celestron handheld digital microscope images of the particles used in laboratory experiments A. E1-E12, B. E14 and E18, C. E16, D. and E13 and E17. Figure S6 – A. Charge surface density 𝝈 calculated considering individual particles in laboratory experiments are spherical. B. Charge to mass ratios calculated for the release of particle masses in laboratory experiments. Figure S7 – A. Charge surface density 𝝈 calculated at Sakurajima and Etna volcanoes considering the objects detected in field experiments are spherical. B. Charge to mass ratios calculated for the same objects assuming a density ranging from 750 kg m-3 to 2700 kg m-3 for Sakurajima, which covers the range from particle clusters to individual ash particles, and a density of 2800 kg m-3 for Etna. The range of possible particle diameters is calculated from the settling velocity using the equation of Bagheri and Bonadonna (2016) (see references in the main text), assuming a variation in sphericity of 0.55 to 1. Data S1 – Sketch used to read voltage and save data to the SD card. Modified from the “Read Analog Voltage” example sketch in the Arduino Documentation (Last revision Nov. 20, 2022 by Killaship). /* ReadAnalogVoltage: Reads an analog input on pin 0, converts it to voltage, and prints the result to the Serial Monitor.Graphical representation is available using Serial Plotter (Tools > Serial Plotter menu). Attach the center pin of a potentiometer to pin A0, and the outside pins to +5V and ground. This example code is in the public domain. https://www.arduino.cc/en/Tutorial/BuiltInExamples/ReadAnalogVoltage */ // Library to communicate with the SD card #include <SD.h> #include <SPI.h> // Count the files on the SD cards to add a new file with name dataXXXX with XXXX the number of files File root; int fileCount = 0; // for counting files int loopCounter = 0; char filename[23]; // Declare filename in this scope String folderPath = "/RESULTS/"; // Specify the folder path String accumulatedData = ""; // Initialize a string to accumulate data // Define the chip select pin for your SD card module const int chipSelect = 10; // the setup routine runs once when you press reset: void setup() { // initialize serial communication at 115200 bits per second: Serial.begin(115200); delay(1000); // Initialize the SD card if (!SD.begin(chipSelect)) { Serial.println("SD card initialization failed!"); return; } // List files in the root directory File root = SD.open(folderPath); // Count the number of files at the root of the SD card: while (root.openNextFile()) { fileCount++; } root.close(); // Generate a unique filename the file for writing // Format the filename with the current counter value // Generate a unique filename with the folder path for writing snprintf(filename, sizeof(filename), "%sdata%04d.txt", folderPath.c_str(), fileCount); // Open the file File dataFile = SD.open(filename, FILE_WRITE); if (dataFile) { Serial.println("File opened successfully"); // Close the file dataFile.close(); } else { Serial.println("Error opening the file"); } // Change the number of bits for analog read analogReadResolution(14); //change to 14-bit resolution delay(2000); //To avoid data lost, delay a period of time to wait for the module to start } // the loop routine runs over and over again forever: void loop() { loopCounter++; // Increment the loop counter // read the input on analog pin 0: int sensorValue = analogRead(A5); // Convert the analog reading (which goes from 0 - 16383) to a voltage expressed in mV (0 - 5000mV): float voltage = sensorValue * (5.0 / 16383.0) * 1000; // Accumulate data in the string String data = String(String(loopCounter) + ";" + String(millis()) + ";" + String(voltage) + "\n "); accumulatedData += data; // Add a newline between data points // Check if the loopCounter is a multiple of 750 if (loopCounter % 750 == 0) { // Open the data file for writing File dataFile = SD.open(filename, FILE_WRITE); if (dataFile) { // Write the accumulated data to the file dataFile.println(accumulatedData); dataFile.close(); accumulatedData = ""; // Clear the accumulated data } else { Serial.println("Error opening data file"); } } delay(1); }