Abstract: An apparatus periodically samples fluid flowing across a surface by providing a plate for mounting flush with the surface. The plate has an aperture extending there through and a tubular body extends from the around the aperture with a passage in communication with the aperture. A sample collection vessel is removably attached to the body to receive fluid passing through the aperture and the passage. A valve member closes the aperture and moves when driven by an electromechanical device. The electromechanical device operates the valve member to alternately open and close the aperture during a defined sampling time to acquire a plurality of samples of the fluid flowing across the surface.