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Here, nonthermal plasma generated by a dielectric barrier discharge (DBD) system was applied to inactivating aerosolized Bacillus subtilis cells and Pseudomonas fluorescens as well as indoor and outdoor bioaerosols. The culturability, viability, and diversity losses of the microorganisms in air samples treated by the plasma for 0.06-0.12 s were studied using culturing, DNA stain as well as polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) methods. In addition, the viable fraction of bacterial aerosols with and without the plasma treatment was also quantified using qPCR coupled with ethidium monoazide (EMA). It was shown that less than 2% of B. subtilis aerosols survived the plasma treatment of 0.12 s, while none of the P. fluorescens aerosols survived. Viability tests, EMA-qPCR results, and Scanning Electron Microscopy (SEM) images demonstrated that both bacterial species suffered significant viability loss, membrane, and DNA damages. Exposure of environmental bacterial and fungal aerosols to the plasma for 0.06 s also resulted in their significant inactivations, more than 95% for bacteria and 85-98% for fungal species. PCR-DGGE analysis showed that plasma exposure of 0.06 s resulted in culturable bacterial aerosol diversity loss for both environments, especially pronounced for indoor environment. The results here demonstrate that nonthermal plasma exposure could offer a highly efficient air decontamination technology.

In this study, airborne MS2 bacteriophages were exposed for subsecond time intervals to atmospheric-pressure cold plasma (APCP) produced using different power levels (20, 24, and 28 W) and gas carriers (ambient air, Ar-O 2 [2%, vol/vol], and He-O 2 [2%, vol/vol]). In addition, waterborne MS2 viruses were directly subjected to the APCP treatment for up to 3 min. MS2 viruses with and without the APCP exposure were examined by scanning electron microscopy (SEM), reverse transcription-PCR (RT-PCR), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Viral inactivation was shown to exhibit linear relationships with the APCP generation power and exposure time (R 2 > 0.95 for all energy levels tested) up to 95% inactivation (1.3-log reduction) after a subsecond airborne exposure at 28 W; about the same inactivation level was achieved for waterborne viruses with an exposure time of less than 1 min. A larger amount of reactive oxygen species (ROS), such as atomic oxygen, in APCP was detected for a higher generation power with Ar-O 2 and He-O 2 gas carriers. SEM images, SDS-PAGE, and agarose gel analysis of exposed waterborne viruses showed various levels of damage to both surface proteins and their related RNA genes after the APCP exposure, thus leading to the loss of their viability and infectivity. Inhalation of microbial aerosol particles can cause various health effects, ranging from moderate respiratory impairments to death (1-3). Studies showed that large-scale infectious disease outbreaks, such as the outbreaks of severe acute respiratory syndrome in 2003 and influenza virus H1N1 in 2009, were triggered by airborne transmission of the viral agents (4-7). To reduce exposure to viruses, various methods have been developed and evaluated, including UV irradiation (8-11), chemical agents (12), electrical fields (13, 14), ion emission (15-18), ozone generation (19), and microwave irradiation (20-23). In recent years, atmospheric-pressure cold plasma (APCP), a low-temperature decontamination technology, has gained increased attention for the inactivation of microbial agents due to its high degree of effectiveness and low cost (24). APCP is known as the fourth state of matter, which consists of free charged ions and radicals moving in random directions. Although APCP has been extensively applied to the inactivation of liquid-borne or surface-borne agents (25-30), only a few inactivation studies exposing airborne microbial agents to APCP have been conducted (31-34). A recent study reported that a significant fraction (Ͼ85%) of airborne bacteria and fungi from both indoor and outdoor environments lost their viability within 60 ms of exposure to APCP (34). Reactive oxygen species (ROS) such as OH· were observed in the plasma produced using the air carrier, and bacterial membrane damage was detected in APCP-treated samples (34). Zimmermann et al. (2011) studied the inactivation of adenoviruses in a liquid suspension using APCP; up to a 6-decimal-log reduction was achieved following a 4-min exposure (35)....

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Plasma technology has some shortcomings, such as higher energy consumption and byproducts produced in the reaction process. However non-thermal plasma associated with catalyst can resolve these problems. Therefore this kind of technology was paied more and more attention to treat waste gas. A hybrid system comprising a non-thermal plasma reactor and nanometer titanium dioxide catalyst was used for benzene removal in the air. The paper described the synergistic effect of ozone and photocatalyst in the plasma reactor. Except of electric field strength, humidity and flow velocity, the synergistic behavior of ozone and photocatalyst was tested. The removal efficiency of benzene reaches nearly 99% when benzene concentration is 600 mg/m 3 , and the removal efficiency of benzene also reaches above 90% when benzene concentration is 1500 mg/m 3 . The plasma reactor packed with photocatalyst shows a better selectivity of carbon dioxide than that without photocatalyst. The final products is mostly carbon dioxide, water and a small quantity of carbon monoxide.