Miniaturized atmospheric pressure glow discharges (APGDs) were generated in contact with small sized flowing liquid cathode systems. As anodes a solid pin electrode or a miniature flow Ar microjet were applied. Both discharge systems were operated in the open to air atmosphere. Hydrogen peroxide (H 2 O 2) as well as ammonium (NH 4 ?), nitrate (NO 3-), and nitrite (NO 2-) ions were quantified in solutions treated by studied discharge systems. Additionally, an increase in the acidification of these solutions was noted in each case. Emission spectra of the near cathode zone of both systems were measured in order to elucidate mechanisms that lead to the formation of active species in gas and liquid phases of the discharge. Additionally, the concentration of active species in the liquid phase (H 2 O 2 , NH 4 ? , NO 3 and NO 2-) was monitored as a function of the solution uptake rate and the flow rate of Ar. The suitability of investigated discharge systems in the water treatment was tested on artificial wastewaters containing an organic dye (methyl red), hardly removable by classical methods non-ionic surfactants (light Triton x-45 and heavy Triton x-405) and very toxic Cr(VI) ions. Preliminary results presented here indicate that both investigated flow-through APGD systems may successfully be applied for the efficient and fast on-line continuous flow chemical degradation of toxic and hazardous organic and inorganic species in wastewater solutions. Keywords Atmospheric pressure glow discharge Á Degradation of hazardous chemicals Á Plasma water treatment processes Á Plasma-liquid interaction

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The miniaturized atmospheric pressure glow discharge (APGD) generated between a solid electrode and a flowing small size liquid cathode (dimension 2 mm) was investigated here using optical emission spectroscopy. The discharge was studied in an open air atmosphere, and the spectral characteristics of the plasma source was examined. Analysed APGD was operated at a discharge voltage of 1,100-1,700 V, a discharge current of 20 mA and gaps between a solid anode and a liquid cathode in the range from 0.5 to 3.5 mm. The emission intensities of the main species were measured as a function of various experimental conditions, including the solution flow rate, the gap between the electrodes, and the concentration of hydrochloric acid. The excitation temperature, the vibrational temperatures calculated from N 2 , OH, and NO bands, and the rotational temperatures determined from band of OH, N 2 and NO, were found to be dependent on these experimental parameters. The electron number density was determined from the Stark broadening of H b line. Additionally, the ionization temperature and degree were calculated using the Saha-Boltzmann equation, with the ion to atom ratio for magnesium (MgII/MgI). The results demonstrated that T exc (H), T vib (N 2 ), T vib (OH), T vib (NO) and T rot (OH) were well comparable (*3,800-4,200 K) for selected plasma generation conditions (gap C2.5 mm, HCl concentration C0.1 mol L -1 ), while the rotational temperatures determined from band of N 2 (*1,700-2,100 K) and band of NO (*3,000 K) were considerably lower. The electron number density was evaluated to be (3.4-6.8) 9 10 20 m -3 and the ionization temperature varied, throughout in the 4,900-5,200 K range.