Non-Thermal Plasma for indoor air treatment: Toluene degradation in a corona discharge at ppbv levels

The use of non-thermal plasma, corona discharge, was studied for indoor air applications. Toluene at a very low to moderate concentration (a few ppbv-1000 ppbv) was used as the target compound. Both degradation of toluene and generation of by-products (intermediates and ozone) were investigated. Because of the very low concentrations implemented in this study, high levels of removal efficiency were reached with very low specific density (a few J L−1). It was found that the polarity of the discharge was the parameter having the greatest influence: at 8.2 ppbv, removal efficiency could reach 98.2% under negative polarity while only 62% removal efficiency was achieved under positive polarity. This result is consistent with the lower ozone concentration in positive polarity and hence the lower plasma reactivity. The relative humidity of the air is another highly important parameter. It was found that the number of intermediates detected at the outlet of the plasma and removal efficiency both increased when increasing the relative humidity from less than 2%-40%. At higher relative humidity, toluene removal efficiency remained on the same order of magnitude (close to 80%), while the number and the amount of intermediates decreased. A higher oxidative rate was expected.