Linear-gradient chamber for exposing field plants to controlled levels of air pollutants

Abstract

A linear-gradient chamber for controlled exposure of plants in the field to air pollutants is described. The ratio of chamber wall to ground area was minimized to reduce the chamber effect. The design of this chamber overcomes some of the difficulties of the circular, open-top chambers currently in use by using a linear concentration gradient of pollutant gas in a rectangular, open-top chamber (7.5 x 3 x 0.6 m). Plants grown in rows are exposed to sulfur gases injected at 20 to 500 cm/sup 3/ min/sup -1/ and ozone at 10 cm/sup 3/ min/sup -1/ diluted with air at 10/sup 8/ cm/sup 3/ min/sup -1/. The concentration gradients along a 6-m length of chamber ranged from 2 to 7 ppM at an injection rate of 500 cm/sup 3/ min/sup -1/ and from 0.07 to 0.16 ppM at 10 cm/sup 3/ min/sup -1/. The coefficient of variation in gas concentration in the chamber is about 0.23, comparable to that in conventional circular chambers. The new chamber allows a greater possibility of statistical regression analysis of the dose-response data because the exposure rate is a continuous variable. Despite the large natural variability in measurements such as dry matter production and a relativemore » insensitivity to H/sub 2/S, the dose-response of snap beans to H/sub 2/S, SO/sub 2/, and O/sub 3/ could be determined because of the flexibility allowed in the treatment of data.« less