Dry diffusion denuder made of porous metal discs was developed for ambient air measurement [18–21]. Recently, a
parallel-plate wet denuder (PPWD) was designed and tested at low concentration of HF (3.57–3.80 ppbv), HCl (0.48–15.63 ppbv), and HNO3 (8.43–20.92 ppbv)