MRI of lung parenchyma is limited by low proton density and susceptibility effects at air-tissue interfaces. Recent high-performance low-field MRI systems have provided a new opportunity to mitigate the latter issue. In this work, we demonstrate a framework for simulating lung MRI across B0 field strengths. We estimate apparent transverse relaxation due to proximity to A) sub-voxel alveoli, and B) bronchial tree. Alveoli are modeled using face-centered cubic close packing. The bronchial tree is modeled using a recent XCAT phantom.