An airborne substance detector includes an air intake that sweeps through a fixed area, and a fan that draws air toward an effluence detection device that analyzes the air for one or more substances, such as explosives. The air intake may be a series of tubes of a rotary gate, with multiple sets of tubes that rotate about a central axis. The fan or blower draws air through holes in the tubes, and through a manifold that directs air to the effluence detection device from a single set of tubes at a time. In addition the detector may include a heater that may enhance vaporization of substances to be detected. The effluence detection device, the manifold, and the fan may be located in an enclosure at the top of the rotary gate. After detection, a decontamination procedure may be initiated to purge the system of the substance that was detected.