UNC Aerosol Smog Chamber
| Figure 1. UNC 270 m3 dual outdoor smog chamber.
Unique features: 1. Large volume to permit long fine aerosol life-times; 2. Dual chamber affords direct control comparisons; 3. Short sampling distances for aerosol sampling; 4. Diurnal natural sunlight and temperature regimes for realistic model testing and development; 5. Unique ability to exchange content of chambers and to mix and react dilute reactants; 6. Remote control of many of the chamber functions like venting, clean air purging, and data acquisition.
Applications: 1. Study of aged atmospheres with an emphasis on fine aerosols; 2. Experiments targeted at secondary organic aerosol formation; 3. Novel particle nucleation experiments.
Location: The chamber was constructed in the spring and summer of 2002; the laboratory under the chamber was constructed and operational in the spring of 2003. It is located at the University of North Carolina Ambient Air Research Facility near Pittsboro (35° 42' latitude, -79° Longitude), North Carolina and is approximately 18 miles south of the main UNC Chapel Hill campus.
Chamber Description: The dual chamber has a Quonset hut (barn shape) design, to reduce the surface to volume ratio from the standard A frame design of the UNC chambers. The width is 8.53 m, the length 9.75 m, and the maximum height is 3.89 m. A suspended 5 mil FEP Teflon (type C) curtain (Livingstone Plastics, Charlotte, NC) bisects the chamber to form two chamber halves. The orientation chamber bisecting center panel is along an axis 117° SE - 297° NW true heading. One chamber is designated the south chamber and has a volume of 138 m3 and the other chamber and designated as north has a volume of 136 m3. The total volume is 274 m3. Original design estimates were 135 m3 per chamber with a total volume of 270 m3. Hence we have often referred to each chamber as having a volume of 135 m3 and a total volume of 270 m3. The surface to volume ratio of each chamber is 1.08. A sphere of equal volume would have a surface to volume ratio of 0.93 and a cube, 1.16.
The chamber is positioned on a concrete pad 8 feet above the ground. A sampling laboratory (3.66m x 6.1 m) is located directly under the chamber. There is a 25.4 cm space between the Teflon film chamber floor and the 1.25 cm thick false ceiling of sampling laboratory. Two 50 ft3/min squirrel cage fans purge this space with outside air. This is done so that laboratory air does not interact with chamber air via small leaks that can develop in the Teflon film floor.
Figure 2a. Attaching chamber film.
The walls of the chamber are made of 5 mil FEP Teflon film and are attached on 1.22 m centers to 4.81 cm o.d. round tubular metal frames that form the superstructure of the chamber. The overlapping film on each metal frame is held in place on the inside of the chamber by a 3.2 mm x 25.4 mm Teflon strip, covered with a similar aluminum strip and screwed into the frame channel (Figure 2) with sheet metal screws.
Figure 2b. Attaching chamber film.
The small projected area of the superstructure frame creates very little shadowing of the sunlight entering the chamber. It also provides a very durable structure. The vertical temperature profile in sunlight at an average temperature of 304K is +/- 2 °C with the extremes in this range existing at the very top and floor of the chambers. The chamber green house effect is on the order of 4-5 °C when ambient temperatures are in the 300 to 310K range.