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Emission of BVOC (Biogenic Volatile Organic Compounds) from plant leaves in response to ozone exposure (O₃) and nitrogen (N) fertilization is poorly understood. For the first time, BVOC emissions were explored in a forest tree species (silver birch, Betula pendula) exposed for two years to realistic levels of O₃ (35, 48 and 69 ppb as daylight average) and N (10, 30 and 70 kg ha⁻¹ yr⁻¹, applied weekly to the soil as ammonium nitrate). The main BVOCs emitted were: α-pinene, β-pinene, limonene, ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and hexanal. Ozone exposure increased BVOC emission and reduced total leaf area. The effect on emission was stronger when a short-term O₃ metric (concentrations at the time of sampling) rather than a long-term one (AOT40) was used. The effect of O₃ on total leaf area was not able to compensate for the stimulation of emission, so that responses to O₃ at leaf and …