To date, numerous studies have investigated the aftertreatment of exhaust gases from fossil-fueled combustors and combustion engines by plasmas as an environmental plasma application. Owing to the high power requirements of environmental plasma, it is difficult to use the plasma alone for aftertreatment; hence, a hybrid process that combines plasma processing with other techniques is required to reduce the overall power consumption. In developing countries, low-cost plasma hybrid processing has attracted considerable attention as an alternative to the selective catalytic reduction NO_x decomposition (De-NO_x) method and wet lime–gypsum SO_x decomposition method. Moreover, reduced catalytic activity can be enhanced by the plasma because of the decreased exhaust gas temperature, owing to the increased combustion efficiency. This paper reviews studies on successful air pollutant decomposition processes using the plasma chemical process with scale-up reactors. First, experimental techniques and block diagrams of various environmental plasma systems are presented. Subsequently, real-world systems of scale-up plasma reactors are described in detail. Several experimental results suggest that the hybrid treatment of particulate matter and dry De-NO_x is very promising from the viewpoint of energy consumption and material recycling. CO₂ treatment is a very important direction for future work in environmental plasma.