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Gases, such as nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H₂S), and sulfur dioxide (SO₂) are known toxic pollutants in the air. However, they are now recognized as important signaling molecules synthesized in animals and humans from arginine, glycine (heme), and cysteine, respectively. At physiological levels, NO, CO, and SO₂ activate guanylyl cyclase to generate cGMP which elicits a variety of responses (including relaxation of vascular smooth muscle cells, hemodynamics, neurotransmission, and cell metabolism) via cGMP-dependent protein kinases. H₂S is also a crucial regulator of both neurological function and endothelium-dependent relaxation through cGMP-independent mechanisms involving stimulation of membrane K_ATP channels and intracellular cAMP signaling. Additionally, NO, CO, and H₂S confer cytoprotective and immunomodulatory effects. Moreover, NH₃ is a …