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Low-power (250-500 mW) pulsed gliding-arc discharge reactors that utilize water sprayed as a fine aerosol into an argon carrier gas have been previously shown to produce molecular hydrogen (H2) and hydrogen peroxide (H2O2) with high energy yields. In this paper, optical emission spectroscopy in the range of 230-1000 nm is used to assess the formation of radicals in the plasma region of the reactor as functions of spatial position and liquid flow rate. Radical intensities of OH (309 nm) were the highest at 10 mm downstream from the point of discharge initiation, and the gradient of the OH radical intensities between 10 and 15 mm was higher for the higher liquid flow rates that correspond to the highest production rates and efficiencies of hydrogen peroxide. These results support the hypothesis that hydrogen peroxide production efficiency increases with rapid OH radical quenching.