## 2 Experimental Setup and Methods  
The time-resolved imaging and OES experiments were carried out using two types of SDBD reactors. The first reactor had a planar high voltage electrode cut into a rectangular shape and made of 20 \(\upmu\)m thick copper foil, while the other reactor had a cylindrical electrode made of a thin tungsten wire with a diameter of 10 \(\upmu\)m. In both cases, the electrode was placed on a dielectric barrier made of a 1 mm thick ceramic plate (100 mm \(\times\) 100 mm). The grounded electrode was placed on the opposite side of the dielectric. The relative positioning of the electrodes on each side of the dielectric is shown in Figure 1. In the planar electrode configuration, the high-voltage electrode was aligned edge-to-edge with the grounded electrode (Figure 1A), while the wire electrode was positioned to extend halfway across the grounded electrode (Figure 1B). The grounded electrode was electrically insulated with resin. The experiment was conducted in ambient air.  
Both reactors were supplied with an AC sinusoidal high voltage with a frequency of 1 kHz and peak-to-peak voltage of 28 kV generated using the Tektronix AFG3101 (Tektronix, Beaverton, OR, USA) coupled with a Trek40/15 high-voltage amplifier (Advanced Energy, Denver, CO, USA) (Figure 1C). The voltage waveform supplied to the reactor was measured using a Tektronix DPO 4104 oscilloscope equipped with a Tektronix P6015A high-voltage probe. Due to amplifier limitations, higher frequencies and voltages were unavailable, as they would introduce distortions to the voltage waveform. When the high voltage was applied to the reactors, the SDBD was generated and a non-thermal plasma developed from the electrodes.  
The morphology of the discharged plasma was studied using an intensified CCD (ICCD) camera, which allowed for a series of plasma images to be taken with very short exposure times (down to 1 ns) over various time delays with respect to the voltage waveform. It should be noted that this imaging technique generates a set of images representing different discharges, rather than tracking a single plasma discharge over time. In the preliminary studies, we confirmed that the plasma structures were repeatable between periods of the voltage waveform. The plasma images were recorded using an Andor iStar DH734 ICCD, synchronized with the function generator and equipped with a UV lens positioned perpendicularly above the reactor at a distance of approximately 50 mm (no additional optical filters were used in the experimental setup). The plasma emission spectra were recorded with two types of fiber-coupled spectrometers: (i) an OceanOptics Maya 2000 (Ocean Optics, Inc., Orlando, FL, USA), which offers a relatively wide spectral range of 200 nm-1100 nm, and (ii) an Andor Mechelle ME5000 (Oxford Instruments, Abingdon, UK), which was selected for high-resolution spectral analysis. Prior to measurements with the Mechelle spectrometer, its calibration curve was determined using a white light source. The optical fiber input for both spectrometers was positioned 10 mm above the reactors 1 mm from the edge of the high-voltage electrode and was used interchangeably with the ICCD camera.  
Figure 1: Geometry of the SDBD reactors with (**A**) planar electrode, (**B**) cylindrical electrode. (**C**) Experimental setup for imaging and OES (for clarity, only a reactor with a planar electrode is shown). The field of view of the ICCD camera is marked with dashed lines.