Influence of spark polarity on the tubular Electrostatic precipitators characterization for CH4 and CO gases

<ns3:p> Methane (CH₄) and carbon monoxide (CO) remain two of the most critical air pollutants due to their significant environmental and health risks. This study investigates the enhancement of pollutant removal efficiency in plasma-based systems by examining how spark discharge polarity affects gas treatment performance under sub-atmospheric pressure. Using a tubular electrostatic precipitator (ESP) operated at 15, 20, and 25 kV and pressures of 380, 406, and 508 Torr, we measured key plasma parameters including discharge current, electron temperature and density, ozone (O <ns3:sub>3</ns3:sub> ) generation, specific energy input (SEI), and gas removal efficiency under both positive and negative polarity conditions. Our results show that higher electron temperatures and discharge currents increase the availability of energetic electrons capable of enhancing molecular dissociation and pollutant removal. Negative polarity produced a more active plasma, yielding maximum removal efficiencies of 88% for CH₄ and 87% for CO at 25 kV and 380 Torr, driven by intensified formation of reactive species such as O•, OH•, and O <ns3:sub>3</ns3:sub> that promote oxidative degradation. SEI increased with voltage, reaching 873 J/L under optimal conditions, in close correlation with peak removal performance. The system exhibited a 20.3°C rise in outlet gas temperature within 120 seconds, indicating substantial energy deposition while maintaining non-thermal plasma behavior. These findings demonstrate that pollutant removal in ESP systems is governed primarily by plasma-chemical reactions rather than electrostatic collection, and they provide a practical pathway for optimizing spark-driven ESP reactors for indoor air purification applications targeting low concentrations of CH₄ and CO. </ns3:p>