<p>Fixation of nitrogen and the generation of plasma-activated water are currently a significant focus within the low-temperature plasma research community. This study examines the enhancement of nitrogen fixation in water, by converting the weakly soluble nitrogen oxides (NO and NO₂) generated by transient spark (TS) to highly soluble dinitrogen pentoxide (N₂​O₅​) and nitric acid (HNO₃​) in the&#xa0;gas phase. This is achieved by mixing ozone (O₃) with air that has been treated by a TS discharge. Without O₃, only nitrite ions (NO₂⁻)​ are detected in the water, formed primarily due to reaction between solvated NO and NO₂. With addition of O₃ (400&#xa0;ppm), the composition of species in water significantly changes depending on the initial NO/O₃ ratio. An excess of O₃ enables formation of N₂​O₅​ and HNO₃​ in the gas and a high concentration of nitrate ions (NO₃⁻​) in the water. With an excess of NO, the dominant gas phase product is NO₂ and a mixture of NO₂⁻ and NO₃⁻ is formed in the water by reaction between solvated NO₂ molecules. Despite the additional energy required for O₃​ generation, the overall energy efficiency for the formation of NOx​⁻ (NO₂⁻​ + NO₃⁻​) in the water increases fourfold, when enough N₂O₅ is formed. Further improvements are possible by optimizing the use of O₃​ and ensuring all N₂​O₅​ is captured from the gas phase.</p>