A novel atmospheric pressure plasma device releasing atomic hydrogen has been developed. This device has specific properties such as (1) deactivation of airborne microbial-contaminants, (2) neutralization of indoor OH radicals and (3) being harmless to the human body. It consists of a ceramic plate as a positive ion generation electrode and a needle-shaped electrode as an electron emission electrode. Release of atomic hydrogen from the device has been investigated by the spectroscopic method. Optical emission of atomic hydrogen probably due to recombination of positive ions, H + (H 2 O)n, generated from the ceramic plate electrode and electrons emitted from the needle-shaped electrode have been clearly observed in the He gas (including water vapour) environment. The efficacy of the device to reduce airborne concentrations of influenza virus, bacteria, mould fungi and allergens has been evaluated. 99.6% of airborne influenza virus has been deactivated with the operation of the device compared with the control test in a 1 m 3 chamber after 60 min. The neutralization of the OH radical has been investigated by spectroscopic and biological methods. A remarkable reduction of the OH radical in the air by operation of the device has been observed by laser-induced fluorescence spectroscopy. The cell protection effects of the device against OH radicals in the air have been observed. Furthermore, the side effects have been checked by animal experiments. The harmlessness of the device has been confirmed.
Recently the presence of free radicals, in particular OH in indoor environments has received an increasing concern 1-3 . It was reported that the OH radical initiates a complex series of reactions that generate still other radicals and ultimately produce species that can adversely affect human health in indoor environments 1 . We have developed novel atmospheric pressure plasma device that generates atomic hydrogen to neutralize OH radical in indoor air. Device structure and formation of atomic hydrogen in the device have been reported in our previous paper 4 . The purpose of this paper is to report the observation of OH radical reduction with the operation of this device by using spectroscopic and biological methods. Cell protection effects of the device from OH radicals in the air are reported. In the spectroscopic experiments, OH radicals were produced in the air by a dielectric barrier discharge. The laser-induced fluorescence (LIF) spectroscopy was employed for monitoring of the OH radical concentration. When the device was operated the OH-LIF intensity was remarkably reduced. In the biological experiments, we compared the cell death rate between cells exposed to reactive oxygen species with or without the device in operation. The operation of the device reduced the cell death caused by the OH radicals produced in the air by dielectric barrier discharge as well as the death induced by hydrogen peroxide produced enzymatically in the culture medium.1. C.
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