Abstract
Flue-cured tobacco (Nicotiana tabacum McNair 944) was exposed to chronic doses of ozone (O/sub 3/) in open-top field chambers to determine the influence of frequency and magnitude of peak O/sub 3/ concentrations and daily exposure duration on tobacco yield response. The treatments were established by adding O/sub 3/ in amounts that were proportional to ambient O/sub 3/ concentrations or in constant amounts. The frequency of occurrence and level of peak O/sub 3/ concentrations were greater for each proportional-addition treatment than for the corresponding constant-addition treatments. However, the seasonal mean O/sub 3/ concentrations were nearly identical, and the yield response to O/sub 3/ was similar for both types of O/sub 3/ for 12 hr/day (1000 to 2200 hours EDT) was 10% less (three treatment levels combined) than in those receiving proportional addition for 7 hr/day (1000 to 1700 hours EDT). If other important crop species have a similar response to O/sub 3/ late in the afternoon, previous national crop loss estimates based on seasonal 7 hr/day O/sub 3/ exposures may be low.
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