Design and Performance of an Exposure System for Measuring the Response of Crops to Acid Rain and Gaseous Pollutants in the Field

During 1982-1984, experiments regarding the nature of crop responses to combinations of acid rain and gaseous pollutant treatments were conducted. Open-top field chambers were used in conjunction with an automatic rain exclusion-simulant distribution system to expose crops to controlled levels of gaseous pollutants and rain acidity in a field setting. Rain exclusion was achieved by automatically moving covers over the experimental plots at the onset of a rain event. The simulant distribution system was automatically activated after 0.25 mm of rain was collected in a recording rain gauge located adjacent to the experimental plots. Rain simulants were dispensed through nozzles until the amount deposited within the plot equaled that deposited by the natural rain outside the plot. The system was capable of dispensing rain simulants with three levels of acidity to ambient air plots and to charcoalfiltered and nonfiltered-air chambered plots. The ability to automatically dispense rain simulants during, and in e...