Optical Emission Spectroscopy of High Voltage Cold Atmospheric Plasma Generated Using Dielectric Barrier Discharges

While numerous experiments have demonstrated the efficacy of high voltage cold atmospheric pressure plasmas for extending food shelf-life and sterilizing medical instrumentation in sealed packages, the influence of the packaging material and gas composition on the reactive gas species generated by the high voltage atmospheric cold plasma is poorly understood. This study elucidates the impact of these parameters on plasma generation in sealed packages for four gases (ambient air, commercial grade compressed air, and high purity helium and nitrogen) placed in commercially available transparent plastic containers and bags. After adequate gas flushing, we observed that the container and bag individually reduced signal intensity by 63% and 45% across the measured wavelengths of 200 nm to 1100 nm, demonstrating that they acted as broadband absorbers. Neither the container nor bag influenced the wavelengths of the peak emissions, only the amplitude, indicating no significant effect on the types of species generated. Lissajous diagrams showed that the power dissipated by the nitrogen and ambient air plasma generated at 72 3.7 kV RMS were comparable to the compressed dry air discharge generated at 80 3.7 kV RMS. The helium discharge at 37 3.7 kV RMS absorbed approximately 92% more power than these gases. We observed translational temperatures ranging from 1088 K for nitrogen to 1421 K for compressed air and rotational temperatures ranging from 285 K for helium to 479 K for compressed air. These results indicate that packaging materials have minimal effect on the most dominant peaks although further studies are required to elucidate the impact on less intense peaks observed

Cold Atmospheric Pressure Plasmas for Food Applications

Successfully distributing shelf food requires treatment to eliminate microorganisms. Current chemical methods, such as chlorine wash, can alter food quality while only being effective for a limited time. Cold atmospheric pressure plasmas (CAPs) can eradicate the microorganisms responsible for food spoilage and foodborne illness. Optimizing CAP treatments requires understanding the reactive species generated and relating them to eradication efficiency. Recent studies have used optical emission spectroscopy (OES) to determine the species generated in a sealed package that would hold food. In this study,we supplement the OES results with optical absorption spectroscopy (OAS) using the same gases (helium, nitrogen, compressed air, humid air) to elucidate plasma chemistry and temperature. We first reproduce previous results using a new setup while assessing the impact of the package and surrounding box on the plasma spectrum. A UV-Vis light lightsource is emitted through a series of lenses placed next to the plasma. Analysis using SpecAir software allows the identification of absorbed peaks and the calculation of rotational, vibrational, and electron temperatures. Results show that the air plasma produces a primary absorbance peak at a wavelength of ~260 nm, demonstrating the diagnostic capability of this technique . Species generation declined dramatically during the first two minutes of treatment with the effect leveling off thereafter. These findings elucidate reactive species generation within the plasma to optimize CAP systems for microorganism decontamination

Optical Emission Spectroscopy Diagnostics of Cold Plasmas for Food Sterilization

There is a growing need for economical, effective, and safe methods of sterilizing fresh produce. The most common method is a chlorine wash, which is expensive and may introduce carcinogens. High voltage cold atmospheric pressure plasmas are a promising solution that has demonstrated a germicidal effect; however, the responsible chemical mechanisms and reaction pathways are not fully understood. To elucidate this chemistry, we used optical emission spectroscopy to measure the species produced in the plasma generated by a 60 Hz pulsed dielectric barrier discharge in a plastic box containing various fill gases (He, N2, CO2, dry air, or humid air). In addition to estimating chemical species concentrations, we performed preliminary calculations of electronic, vibrational, rotational, and translational temperatures