A parallel plate wet denuder (PPWD) was designed and tested for acidic gas absorption in this studY. The PPWD is composed of two fi-osted glass plates coated with nano-TiO? particles. The gap of the plates is 4 inin, the active sinjace is 7.5 cut in width and 15 cin in height. The DI water is,flowing downward along the sulf ces to form a icn forni tvaterfilm to absorb the gas.flowing uptvard along the gap. The gas absorption efficiency and nienzory eft ct were tested using test gases of HF (3.573.80 ppb), HCl (0.48-15.63 pph), and HN03 (8.43-20.92 ppb) generatedfi-oni per"leation tubes at the flow rate of 5-10 Llinin, scrubbing DI water flow rate oj'].O n?Llnlilll plate, and PH = 6.8 -_ 0.3. The experiment was also conducted for HF and HCl with scrubbing water PH value ol'3.08 and 4.10 to examine the ffcct of PH oil the absorption efficiency. The experimental data at different.flow rates match with the theoretical values ver ' N7 well assuming peifect absorption condition (it the water filin when the scrubbing water PH = 6.8 +/- 0.3. The absorption efficiency of the three gases at the sampling flow rate of 5 Llinin was nearly 100% when the scrubbing water PH value was 6.8 +/- 0.3, but was ' found to decrease slightl ' v when the PH value of scrubbing tvater was reduced from 6.8 to 3.08, which indicates slight inodification of' peifect absorption condition at the water filin. The meniory cffect test showed that the rise time was 15 to 25 min and the fiall tinie was 10 to 25 iniiijbi- the three gases. Good un ft)rniit_v Qfthe tvater filin was observed during the 9-day ainbient air sampling for HF, 110, and HNO,, which indicates the applicabilitly (the present PPWD for ambient air sampling. (c) 2008 American Institute of Chemical Engineers.