The data are biomass measurements from an ozone exposure experiment, during which Trifolium repens and Lolium perenne were exposed as both monocultures and two-species mixtures to an episodic rural ozone regime in large, well-watered containers within solardomes for 12 weeks. Treatments were elevated ozone (AOT40 (Accumulated Ozone Threshold exposure of 40 parts per billion) of 12.86 ppm h) or control conditions (AOT40 of 0.02 ppm h). Measurements were dry weight, with a cutting height of 7cm above soil level. The distribution of plant material within the canopy was determined by separating material growing in the upper canopy (>14cm) from the canopy edge and the inner canopy for both species. The experiments were carried out in the CEH Bangor Air Pollution Facility. Work was funded by the Centre for Ecology & Hydrology Integrating Fund Initiative. The observed decreases in photosynthetic efficiency and capacity in elevated ozone indicate that the ability of such ubiquitous vegetation to act as a sink for atmospheric carbon may be reduced in future climates. Full details about this dataset can be found at https://doi.org/10.5285/5de90f7a-dec9-4bd5-af52-d0873a09d25d