A duct can be configured to receive a denuding gas flow. A solid denuding surface that is connected to a drive system can be configured to move the solid denuding surface within the duct while the solid denuding surface is continuously concentrating one or more gas-phase species from the denuding gas flow on the denuding surface. Also, a denuding gas flow can be passed along a denuding surface to concentrate one or more gas phase species from the denuding gas flow onto the denuding surface with a diffusion denuding action. The denuding surface can be moved while continuing to concentrate the one or more gas phase species from the denuding gas flow onto the denuding surface.