Bruce Bégout (born in 1967) is one of the most original figures in contemporary French phenomenology. Both writer and philosopher, he first evokes diverse “ambiances” in his literary work before advancing a phenomenology in which “air” is the primary medium of experience and sense of smell the privileged access to ambiance. In Le concept d’ambiance: Essai d’éco-phénoménologie [The concept of ambiance: Essay in eco-phenomenology], he distinguishes three ways of approaching such phenomena—dialogical, synthetic, and autochthonous—and adopts the autochthonous stance, which treats ambiance as an autonomous, a priori, atmospheric field felt rather than seen. I first summarize these distinctions, and then situate his own autochthonous, from-within account within the phenomenology of atmosphere, showing how it reframes rationality by treating some objects of knowledge as inherently ambiguous and resistant to objectification. Finally, I argue that, for Bégout, “ambient sense of smell” (flair ambianciel), as a function of breathing, discloses the tone of situations more immediately than vision—clarifying why the air we co-breathe grounds our primary experience of ambiance.