As shown in Fig. 5, an increase in the liquid flow rate increases the removal efficiency of the PPWS. When Ql/Qg is increased from 1.85 to 3.7 L/m3 , the removal efficiency of the PPWS with the MPPM is found to increase from 93.9–96.7% to 96.7–99.9% for HCl, 85.1–96.0% to 95.3–99.5% for HNO3, and 59.7–82.9% to 91.5–98.4% CH3COOH for the inlet concentration of 0.02–2 ppmv