Reduced ozone by air filtration consistently improved grain yield in wheat.

This study considered effects of reduced [O(3)] on wheat yield. Open-top chamber charcoal filtered air treatments were compared with non-filtered treatments for field-grown wheat. 30 experiments meeting requirements were found, representing nine countries in North America, Europe and Asia. 26 experiments reported improved yield and 4 experiments reduced yield by filtration, a significant positive effect. Average yield improvement was 9%. Average daytime [O(3)] was reduced by filtration from 35 to 13 nmol mol(-1). Filtration efficiency was 63% for O(3) and 56% for SO(2). For NO(x) it was observed that NO(2) was reduced and NO increased by filtration. Thus, filters convert NO(2) to NO. Most experiments reported low or very low [SO(2)] and [NO(x)]. Thus, O(3) can be concluded to be the main phytotoxic component in the experiments. Elevated [NO(2)] was observed in one experiment. The conclusion is that current [O(3)] over large parts of the world adversely affect wheat yield.