Penicillium digitatum spores were inactivated using an oxygen-radical source that supplies only neutral oxygen radicals. Vacuum ultraviolet absorption spectroscopy was used to measure the ground-state atomic oxygen [O (3Pj)] densities and they were estimated to be in the range of 1014–1015 cm-3. The inactivation rate of P. digitatum spores was correlated with the O (3Pj) density. The result indicates that O (3Pj) is the dominant species in the inactivation. The inactivation rate constant of P. digitatum spores by O (3Pj) was estimated to be on the order of 10-17 cm3 s-1 from the measured O (3Pj) densities and inactivation rates.

The effectiveness of atomic and excited molecular oxygen species at inactivating Penicillium digitatum spores was quantitatively investigated by measuring these species and evaluating the spore inactivation rate. To avoid the effects of ultraviolet light and charged species, a non-equilibrium atmospheric-pressure radical source, which supplies only neutral radicals, was employed. Ground-state atomic oxygen (O(3Pj)) and excited molecular oxygen (O2(1Δg)) species were measured using vacuum ultraviolet absorption spectroscopy. The inactivation rate of spores was evaluated using the colony count method. The lifetimes of O(3Pj) and O2(1Δg) in an argon gas ambient at atmospheric pressure were found to be about 0.5 ms and much more than tens of ms, and their spore inactivation rates were about 10−17 cm3 s−1 and much lower than 10−21 cm3 s−1, respectively.

A non-equilibrium atmospheric pressure plasma jet excited by 60-Hz ac power was diagnosed by laser Thomson and laser Raman scattering. We obtained the spatial distributions of the electron density, electron temperature, and gas temperature. The results show that the plasma can generate an electron density of up to 1021 m-3, an electron temperature of approximately 1 eV, and a gas temperature as low as approximately 700 K, indicating that the plasma is in the non-equilibrium state. The laser scattering diagnostic method and the obtained data are useful in the application of the non-equilibrium atmospheric pressure plasma jet.

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