## 2 Materials and Methods
To observe the light emission from multiple species at once and evaluate the production of the OH and NO species in the plasma a broad-band optical emission spectroscopy (OES) in the wavelength range from 200 nm to 750 nm was performed using a multi-channel spectrometer from Avantes (model AvaSpec-ULS2048X64T), with spectral resolution (FWHM) equal to 0.76 nm. More precise spectroscopic measurements in the 730-840 nm range were made with a multi-channel spectrometer from Horiba (model MicroHR), with FWHM equal to 0.42 nm, which is aimed to monitor mainly the line emissions from the O I (\({}^{5}P\rightarrow{}^{5}S\)) triplet at \(\lambda\) = 777 nm and estimate the production of atomic oxygen in the plasma jet. For both spectrometers, the light emitted by the plasma jet was collected using optical fibers placed parallel to the surface target. The collection scheme is depicted in Figure 1b. Both optical fibers have numerical apertures (NA) of 0.22, and were placed in the same plane at 90 degrees each other. The only relevant difference between the optical fibers is in their core diameters-1000 \(\upmu\)m for that connected to the Avantes spectrometer and 100 \(\upmu\)m for the other. The distance x between the center of the plasma column and the fiber optic light input are also the same and equal to 5 mm, so, by combining the x value, NA and core diameters of the optical fibers, the lengths of the plasma jet seen by each optical fiber are approximately 2.5 mm and 1.6 mm long for the Avantes and Horiba spectrometers, respectively. Due to the absence of absolute calibration of the spectral intensity of the spectrometers employed to measure the intensities of emissions of lines and bands of the spectra, the analysis of the production of reactive species will be more qualitative than quantitative. However, we can use the relationship between intensity of emission and density of emitting species (\(I_{specie}\) and \(n_{specie}\), respectively) to assess the number of species produced in the plasma, i.e. : \(I_{specie}\propto n_{specie}\). Spectroscopic measurements were also used to obtain rotational and vibrational temperature values (\(T_{rot}\) and \(T_{vib}\), respectively) of N\({}_{2}\) molecules. To obtain those \(T_{rot}\) and \(T_{vib}\) values, we used spectroscopic emissions from the N\({}_{2}\) second positive system, \(C^{3}\Pi_{u},\
u^{\prime}\to B^{3}\Pi_{g},\
u^{\prime\prime}\) (referred as \(N_{2}\)(\(C\to B\)) hereafter), with \(\Delta\
u=\
u^{\prime}-\
u^{\prime\prime}=-1\), in the wavelength range from 345 to 360 nm [33; 34; 35; 36]. Spectra simulations were performed using the massiveOES software [37; 38]. Thus, comparisons between measured and simulated spectra are performed and temperature values are determined by those that generate simulated curves that best fit to the experimental spectra. The spectral resolution provided by the Avantes spectrometer is not sufficient to resolve the rotational levels of the N\({}_{2}\) molecules, which is a requirement to obtain accurate values for the \(T_{rot}\) parameter. However, there is a direct relationship between the shape and broadening of the N\({}_{2}\) vibrational bands and the variation of the \(T_{rot}\) values, being that the higher the \(T_{rot}\), the larger the broadening and the higher the intensity of the rotational lines in the vibrational bands. Both effects cause a change in the shape of the vibrational bands in that part that degrades to violet, causing it to become higher and wider, allowing the estimation of the \(T_{rot}\) values usinglow-resolution spectrometers. Thus, even not very accurate, the obtained \(T_{rot}\) values can be good enough to show the trend of that parameter. It is important to notice that the spectroscopic measurements used to obtain \(T_{rot}\) were performed in close proximity of the target surface. Therefore, in this case, the \(T_{rot}\) values may be different from the \(T_{gas}\) ones [34].