Plasma chemistry model of surface microdischarge in humid air and dynamics of reactive neutral species

We present a numerical model of a surface microdischarge (SMD) in humid air at atmospheric pressure. Our model includes over 50 species and 600 elementary reactions and consists of two, coupled well-mixed regions: a discharge layer with both charged and neutral species and an afterglow region consisting only of neutral species. Multiple time steps employed in our model enable capturing rapid dynamic behaviour in the discharge layer as well as the relatively slow diffusion and reaction in the afterglow. A short duration, high electric field is assumed to be excited at 10 kHz in the discharge region with power density maintained at 0.05 W cm(-2). Among the predicted dominant species in the afterglow are O-3, N2O5, N2O, HNO3, H-2, NO3, H2O2, HNO2 and NO2. The results are in qualitative agreement with Fourier transform infrared absorption spectroscopy. Our simulation results show that density of those reactive species continues to evolve significantly in time, even after similar to 15 min of SMD exposure. This result suggests that SMD treatments on the order of minutes or less may involve significant neutral species concentration and flux transients, potentially affecting interpretation of results.