Research Projects

Project at a Glance

Project Status: complete

Title: Documentation of ozone as the primary phytotoxic agent in photochemical oxidant "smog".

Principal Investigator / Author(s): Olszyk, David M.

Contractor: University of California, Riverside

Contract Number: A6-125-32

Research Program Area: Atmospheric Processes, Ecosystem & Multimedia Effects

Topic Areas: Ecosystem Impacts, Impacts, Monitoring


The Statewide Air Pollution Research Center has a continuing mission to investigate the effects of air pollution on agricultural crops, native vegetation, and forests; and to determine the amount of loss being caused by these pollutants. To further this mission we have conducted the pilot study. Documentation of Ozone as The Primary Phytotoxic Agent in Photo-chemical Oxidant "Smog". The study evaluated whether equivalent ozone concentrations in ambient oxidant "smog" produce the same physiological, growth plants. The study used three treatments charcoal-filtered air (CF), non-filtered and added ozone in filtered air yield, and injury effects in open-top field chambers: air (NF), and filtered air plus added ozone to equal the ozone concentration in the ambient chambers. l Outside (ambient air, i.e. AA) plots served as controls for the non-filtered chambers to evaluate any chamber effect on the plant response to ozone. The added ozone was dispensed from an ozone generator equipped with dry air or oxygen. Ozone was added according to the same temporal pattern as the ambient ozone via a computer feedback system. Alfalfa was the test plant with two cultivars in the chambers, the ozone susceptible cultivar. "Mesa Sirsa," and tolerant cultivar "Eldorado." Physiological measurements for the alfalfa included pigment analysis (chlorophyll and carotenoids) and gas exchange (stomata1 conductance and transpiration). Growth, yield, and injury measurements included height, fresh weight, dry weight, and percentage empty nodes per stem. This study indicated that ozone is the primary agent in phytotoxic effects of photochemical oxidants. This was demonstrated by the similar plant responses in the O3 and NF treatments including necrotic injury symptoms, enhanced lower leaf senescence, stomatal closure, leaf pigment degradation and decreased growth and yield. For most parameters there were no statistically significant differences between the O3 and NF treatments. However, the study also indicated that in addition to the general similarities in response between the O3 and NF treatments, detrimental effects were increased with generated ozone compared to ambient ozone. The O3 treatment resulted in significantly greater leaf injury, and chlorophyll concentrations, and a distinct trend toward a larger reduction in dry weight than for the NF treatment. There were no differences in stomatal conductance and transpiration between the 0 3 and NF treatments. These results also indicated that use of dry air to generate ozone may overestimate losses due to ambient ozone. Conversely, use of oxygen to generate ozone may underestimate losses due to ambient oxidants, as other detrimental oxidants such as nitric acid vapor are not present as they would be in ambient air. Both the ambient and added ozone treatments indicated that ambient oxidants produced yield and growth reductions, leaf in jury, stomata1 closure, and lower leaf pigment concentrations compared to CF air as seen in previous studies. Significant chamber effects on growth and yield also were observed, with less intense yield, growth, and injury effects from ozone in NF air than in ambient air (outside) plots. This information will aid in the interpretation on past and current controlled studies where ozone is added to chambers to simulate different ambient oxidant concentrations, and studies where ozone in ambient air was assumed to be the phytotoxic air pollutant in the photochemical "smog" complex.


For questions regarding research reports, contact: Heather Choi at (916) 322-3893

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