Quantify small air currents in a somewhat controlled environment

How can I measure how much air turbulence exists in a volume of roughly 0.5m³? There is sensitive manual equipment that operators need to manipulate, so I can't put it in a vacuum or sealed vessel, (and I just need to measure, not minimize). The equipment is on a vibration isolated table in a temperature controlled environment with HEPA filters and basic care taken to ensure no air vents are pointed at the system. This isn't a clean room, but I can't use something like powder or smoke to visualize air movement.