A novel approach has been undertaken to develop a high efficiency compact diffusion denuder utilizing a porous metal disc. The performance of a porous metal disc used as a compact diffusion denuder has been experimentally and theoretically evaluated. The porous media is made of 100 μm grade sintered stainless-steel. The disc is 4.7 cm in diameter and 0.23 cm in thickness. Experiments showed that it has high gas collection efficiency and low particle loss at 10 liter per minute (1 min-1). Using 1% sodium carbonate/glycerin coating, the collection efficiencies for the sulfur dioxide and the nitric acid gas are 99.6 ± 0.4% and 93.4 ± 2.5%, respectively. Comparisons to an annular denuder sampling simultaneously are found to be 106.3 ± 6.0% and 95.5 ± 15.8% for sulfur dioxide and nitric acid gas, respectively. The averaged loss for monodisperse aerosols in the particle size range of 0.015-2.5 μm in diameter is under 10%, with loss of less than 3% in the important size range of 0.1-2.5 μm. The sampling capacity of the denuder for 25 ppb sulfur dioxide at 101 min-1 is over 100 h. Membrane filtration theory was used to model the gas collection efficiency and particle losses. The result indicates that the porous metal used as a denuder is very efficient in collecting gas. Also, the small size of the denuder makes it possible to design a very compact atmospheric and/or indoor denuder sampling system.