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Characteristics of Air Exclusion Systems vs. Chambers for Field Air Pollution Studies¹

ABSTRACT

An air exclusion system was designed, constructed, and tested to determine its effectiveness in studies of air pollutant effects on vegetation. The air exclusion system was shown to be an effective alternative to open-top field chambers for controlled exposures of air pollutants to low growing plants. The system design included particulate and activated charcoal filters, pressure-type blowers, a mixing manifold, and perforated inflatable ducts that were positioned between rows of plants. Tests with CO as a tracer gas indicated optimal system parameters for air exclusion including: air flow of at least 0.944 m³ s^–1 within the ducts, three or four rows of holes on the side of each duct pointing 45° upward, 90° to the side, and 45° downward from the center of the duct, four ducts per system, and a hole size that provided an air velocity of 0.5 to 1.8 m s_–1 over the plant canopy. Reductions of > 70% in ambient O³ concentrations could be achieved over the plant canopy at 0.25 m above the ground with the air exclusion system under optimum conditions (low ambient wind speed and high ambient ozone concentrations). This was comparable to the reductions achieved with either open-top or closed-top chambers. A gradient in ozone concentrations was obtained within a single system by delineating the ducts into three sections with different sized holes. Sulfur dioxide was added to a modified system to provide a gradient of 0, 0.03, 0.07, and 0.15 µL SO₂ L^–1 over a winter growing season. No large environmental differences were found between air exclusion systems and open-top chambers vs. outside plots in the summer. In the fall and winter, open-top chambers had higher air, leaf, and soil temperatures than air exclusion sytems or outside plots. Air speed over the plant canopy was higher with the air exclusion system than in open-top chambers or outside plots.

Key Words: environment • open-top chamber • O₃ • SO₂

¹ Contribution from the Statewide Air Pollution Research Center, Univ. of California, Riverside., CA 92521. Research supported in part by the Electric Power Research Institute under Contrast NP 1908-3, and, in part, by the California Air Resources Board under Contrast A3-057-03 and A2-116-33. Mention of a product does not constitute a guarantee or warranty by the Univ. of California, Electric Power Research Institute or California Air Resources Board, and does not imply endorsement of it to the exclusion of other products.

² Assistant Research Plant Physiologist, Staff Research Associate, Staff Research Associate, Assistant Research Plant Chemist, Laboratory Assistant, and Research Biochemist, Statewide Air Pollution Research Center, Univ. of California, Riverside, CA, respectively.

Received for publication September 30, 1985.