1 Introduction 1 Principles for a functional exposure system 2 CSTR design and construction 3 Pollutant (gas) dispensing unit 3 CSTR exposure chamber 5 Shared-time gas-monitoring unit 12 Performance data 15 Greenhouse system 16 Phytotron system 19 Discussion 24 References 25 Appendix.-Materials and costs for the CSTR chamber systems 26 (Phytotron) at Raleigh, N.C. The authors give special thanks to Hugo Rogers for technical suggestions regarding his original system and our proposed designs; and to R. J. Downs, V. P. Bonaminio, and the Phytotron staff for their help and advice on the Phytotron system. We thank Tommy N. Gray for technical assistance and Hans K. Hamann for statistical analyses. We appreciate the assistance of Marvin W. WiUiams with photography and E. P. Stahel for his suggestions on performance concepts. ABSTRACT The continuous stirred tank reactor (CSTR) system utilizes a dynamic, negative-pressure, single-pass airflow for maintaining plants in a uniformly mixed exposure chamber (reactor) to study their response to gaseous air contaminants. Uniform mixing within the chamber is kept constant, regardless of inlet air velocity, by a 135-r/min impeller. Dispensing units, by means of rotameters and flow dilution for gases or calibrated syringe pumps for liquids, maintain constant gas concentrations within the chambers. The dispensing and chamber units are integrated with a shared-time monitoring unit for determination of gas (vapor) concentrations within the chambers. Rates for gas uptake, net photosynthesis, and transpiration can be determined by monitoring inlet and outlet gas streams. CSTR systems for use in environmental growth rooms utilize chambers designed for control of temperature, humidity, and light. CSTR systems for use in a greenhouse do not have environmental controls, but they do have high-intensity lamps so that a minimum light intensity can be maintained. Minor design modifications should permit use of the CSTR systems in the field. Performance data suggest that the CSTR design is superior to other chamber systems presently used for controlled exposures of vegetation to air pollutants.

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A 4.66‐m diam., 3.6 m tall, cylindrical open‐top field chamber was designed, constructed, and tested as a tool to measure the effects of air quality on plant function and yield. It is a larger version of the 3‐m diam. chamber that has been used to measure the effects of gaseous pollutants on crop plants. The new chamber has an aluminum‐channel frame covered with clear polyvinyl chloride plastic film. It is equipped with a frustum (truncated cone) that decreases ambient air ingress and can be fitted with a device to exclude rain (rain cap) for studies with simulated rain pH. During the daylight hours, the mean air temperature within the chamber was 0.6 °C greater than ambient on cloudy, cold days, 2.2 °C greater than ambient on partly cloudy, cool days, and 2.8 °C greater than ambient on sunny, warm days. The mean dew point temperature for a wide range of conditions was 0.7 ° greater inside than outside. Mean solar radiation in the chamber, with new plastic panels, was 15% less than ambient with a rain cap and 12% less with no rain cap. Charcoal filtration removed 78% of the O3 in ambient air; long‐term measurements during charcoal filtration showed that the mean O3 concentration in the chamber (all positions and heights) was 77% less than ambient suggesting little or no long‐term ingress through the top. Short‐term gradients in O3 concentrations existed (mostly near the top of the chamber) during infrequent periods of strong winds. During addition of approximately 0.09 µL L−1 of O3 to nonfiltered air, the mean (14‐d) O3 concentrations across all positions and heights varied by less than 0.005 µL L−1 of the overall mean.

Soybeans, Glycine max (L.) Merr. ‘Davis’, were exposed for 7 h day−1 (111 days) to six concentrations of ozone (O3) and for 4 h day−1 (101 days) to four concentrations of sulfur dioxide (SO2), singly and in mixtures (24 combinations). The pollutant concentrations were selected to span those that occur in major soybean production areas of the USA. The pollutant dose‐yield response relationships were modeled using regression analyses and a Weibull model analysis. Both analyses indicated that a dose of O3 typical for soybean production areas (seasonal 7—h day−1 mean of 0.055 ppm v/v) caused a seed weight decrease of 20% compared to a control dose of 0.025 ppm O3. Sulfur dioxide at levels known to exist regionally in the USA (seasonal 4—h day−1 mean of <0.026 ppm SO2) did not cause injury or affect soybean yield. Neither pollutant changed the dose‐response relationships for the other except at high concentrations where the effect of mixtures was less than the additive effects of the pollutants singly. The dose‐response relationships were similar for each of two soil types.