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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Ozone produces a sigmoidal dose-injury response in sensitive tobacco and pinto bean. A definite threshold concentration and presentation time are required before injury is initiated.

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