The Bedford Glossary of Critical and Literary Terms - Ross Murfin 2018
Mood: Defined by some critics as synonymous with atmosphere, by others as synonymous with tone, and by still others as synonymous with both. Atmosphere refers to the general feeling created for the reader or audience by the work at a given point, whereas tone refers to the attitude of the author toward the reader, audience, or subject matter. The atmosphere of a work may be entirely different from the tone, although the two inevitably affect one another. Mood is probably closer to atmosphere than to tone, but, as a general term, it can correctly be applied to either. One could say that an author creates a somber mood, thereby using it as a synonym for atmosphere; one could also say that an author’s mood is somber, thereby using it as a synonym for tone.