Reduced ozone by air filtration consistently improved grain yield in wheat

This study considered effects of reduced O₃] 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 O₃] was reduced by filtration from 35 to 13 nmol mol⁻¹. Filtration efficiency was 63% for O₃ and 56% for SO₂. For NO_x it was observed that NO₂ was reduced and NO increased by filtration. Thus, filters convert NO₂ to NO. Most experiments reported low or very low SO₂] and NO_x]. Thus, O₃ can be concluded to be the main phytotoxic component in the experiments. Elevated NO₂] was observed in one experiment. The conclusion is that current O₃] over large parts of the world adversely affect wheat yield.