The exposure chamber produces approximately uniform plug flow and repeatable conditions with only moderate non-uniformity of flow velocities (e.g., less than 10% range over the cross section at any given mean velocity). In some cases we deliberately create flows with large scale turbulence using obstructions. Non-uniformity of the flow velocities across the width and height are minimized by inducing a long effective path at the inlet (L/D= 54) and outlet (L/D=34) and by use of adjustable dampers to shift flow vertically and horizontally at the inlet side. the long effective lengths are achieved by forcing the air to flow between full-width baffles spaced 15 cm apart. Large scale eddies at the inlet are removed by baffles and by perforated sheet (90% opacity, 3mm holes) and "egg-crate" plastic (cell size= 1cm) which extend from wall-to-wall. The outlet plenum is similarly constructed. Temperature gradient effects were minimized by insulating with 3 cm construction Styrofoam sheet.