PAAD was conducted with a microwave plasma source at atmospheric pressure. A schematic of the experimental set-up is provided in Figure . The microwave generator was operated at a frequency of 2.45 GHz (S-band) with a maximum power level of 15 kW. Power transmission was through an R26 rectangular waveguide connected to a shorting plunger and rod tuner for adjusting the electrical field. For operation safety, the plasma was ignited with argon gas. After ignition, the oxygen supply was gradually increased until the target flow rate was achieved, and the argon supply was switched off.