Fourier Decomposition (FD) is able to assess lung ventilation and perfusion in one free breathing measurement without any contrast agent. To establish a ventilation-perfusion (VQ) scan robust measurements and absolute quantification is required. Unlike for absolute perfusion quantification, there has been only little success regarding absolute ventilation quantification using FD MRI. Borrowing concepts from oxygen enhanced imaging a regional alveolar ventilation measurement in free breathing is introduced. This method is compared with Fractional Ventilation (FV) and tested for physiological plausibility by assessment of volunteers in supine and prone position. The results show good agreement with available literature and show a similar gravitational behaviour as FV.