Description
Atmospheric pressure dielectric barrier discharges(DBD) generate strongly non-equilirium plasmas which are characterized by high electron energies and with near ambient gas temperatures, making them efficient sources of reactive oxygen and nitrogen species(RONS) for air treatment applications. In this work, a double mesh DBD reactor consisting of two metallic grid electrodes separated by a glass or quartz dielectric barrier was investigated using a mass spectrometer. The discharge was operated in ambient air under high voltage AC, producing a plasma with transient microdischarges. Particular attention was given to identifying gas-phase species relevant for air sanitation including neutral molecules like (O3,NO2, NO, N2O), positive ions (O2+, N2+, NO+) and short lived radicals and metastable states. Species were sampled directly from the atmospheric pressure reactor into a differentially pumped quadrupole mass spectrometer via 200 μm orifice interface. Threshold ionsation analysis was used to discriminate between parent species and fragmentation products which allwos improved selectivity in complex air plasma chemistry. The mass spectrometer enables direct detection of plasma generated ions as well as selective ionsation of neutrals using controlled electron impact energy (70 eV). Correlation between discharge conditions and species intensities were examined. This study demonstrates the capability of atmospheric pressure plasma with mass spectrometry to provide quantitative insight into plasma induced air chemistry, linking discharge physics to gas phase species dynamics. This approach establishes a diagnostic framework for real time charactersation of DBD driven reactive species relevant to plasma based air sanitation technologies.
Recent TIMS measurements on an atmospheric-pressure SDBD plasma revealed possible evidence of metastable-assisted ionization. By scanning the electron energy in a quadrupole mass spectrometer and comparing plasma-off and plasma-on ionization curves, a significant shift of the appearance potential toward lower energies was observed. In particular, the onset of the m/z = 14 (N+) signal shifted from about 24.3 eV in neutral air to around 15.6 eV under plasma conditions, suggesting excited or metastable nitrogen species generated inside the discharge. Ongoing measurements for m/z = 16, 28, and 32 will further investigate excitation pathways in atmospheric-pressure plasma chemistry.