The partial pressure of CO2 is lowest in:

Ref: Multiple sources, Guyton, 12th edition, Pages 487- 488. 502-503: Khurana, W F Ganong, Review of Medical Physiology, 23rd edition Explanation: Normal PO2 and PCO2 at various sites Atmosphere (sea level) (inspired air Alveoli Pulmonary vein Arterial blood Tissue Venous Pulmonary artery Etpurid Air pO2 160 149-160 100-105 95-100 100 40 40 40 120 pCO2 0.3 (Negligible) 0.3 (Negligible) 40 4O 40 46 45 45 27 *A11 values in 'mm Hg' Note: Expired air pCO2 - 27 (Ref: Guyton Table 39-1) Expired air pCO2 - 32 (Ref: Ganong Figure 34-15. Page 635. 24th edition)