OH radical generation by atmospheric pressure plasma and its quantitative analysis by monitoring CO oxidation

The nonthermal plasma process has been studied to promote chemical reactions for decomposition of gaseous pollutants, or sterilization. This process uses radicals produced in the plasma. One of difficult problems for understanding the plasma process is to measure concentrations of radicals. There are several methods such as LIF (laser-induced fluorescence) or OES (optical emission spectroscopy). These methods require rather complicated measurement system, and it is difficult to conduct a quantitative measurement of radicals using these methods. This paper suggests a new method for the quantitative measurement of OH radicals in a pulsed discharge plasma of argon and H ₂O at atmospheric pressure. We measured the amount of CO₂ produced through oxidation of CO by OH radicals. The experimental results supported that this simple method can be used to measure OH radicals produced in argon. In this experimental work, concentration of OH radicals in the pulsed discharge plasma of H₂ O/Ar was 9.4×10¹⁴ molecules cm^-3 pulse ^-1. Using this method, mechanisms of OH radicals formation in the plasma were studied. In the temperature range investigated in this study (50~150°C), the formation of OH radicals was dependent on the SIE (specific input energy) value and the content of the H₂O, and was decreased with increasing gas temperature