 To test the effectiveness, the study will evaluate how AIR001 affects the blood vessels in the lungs and the function of the heart. This will be done by monitoring changes in Pulmonary Vascular Resistance PVR; from BaselineDay 1 start of study drug to Week 16 of the study. PVR measures the resistance to flow in the blood vessels of the lungs. The study will include other assessments to evaluate the effect of the study drug on PAH, including measurements of exercise ability and evaluations of PAH disease symptoms. 