Design and Performance of a Large, Field Exposure Chamber to Measure Effects of Air Quality on Plants

Abstract

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.