A CHAMBERLESS FIELD EXPOSURE SYSTEM FOR DETERMINING THE EFFECTS OF GASEOUS AIR-POLLUTANTS ON CROP GROWTH AND YIELD

A modification of the chamberless Zonal Air Pollution System (ZAPS) has been developed to permit the exposure of crops to various regimes of exposure to gaseous air pollutants under true field conditions. It provides 12 different levels and patterns of pollutant exposure, simulating a wide range of ambient conditions. The different levels and patterns of exposure are achieved through different rates of discharge of pollutant-enriched gas through manifolds suspended above individual plots. A feature of the layout is that, since the plots are grouped together in blocks of four, wind speed and direction dictate the actual exposure patterns received in any plot. For studies with ozone, O3, enrichment of the ambient air occurs daily between 0700 and 2059 h (PDT). The overall O3 concentration supplied to the manifolds is maintained proportional to that in the ambient air, except during the first 3 and the last 3 h of each enrichment period when enrichment is slowly increased and decreased, respectively, to provide smooth transitions from and to the ambient level. Additional control progressively reduces enrichment at low wind speeds. Over a season, the ZAPS results in typical unimodal distributions of concentrations on each plot, with good vertical mixing and reasonable horizontal distributions achieved by the large numbers of discharge orifices in the manifolds. Summary results from two seasons' experiments with processing peas are presented to provide examples of the use of the ZAPS to determine crop yield responses to ozone, based on simple linear regressions of yield against two different exposure indices. © 1990.