This is something that’s always meant a lot to me and that I’ve thought about for a long time but have always had enormous difficulty describing. I call them “ambiances”, and the following author refers to them as “atmospheres”. At least, I think he and I are talking about the same thing ― I’m never completely sure.
Ambiances are a kind of feeling. They’re the subtle, visceral, pervasive, indirect, ever-present, ever-changing, background ‘tinges’ or ‘timbres’ or ‘undertones’ of life. In a lot of ways they’re similar to emotions (happiness, sadness, fear, etc.) and sensations (colors, scents, etc.), and they’re intertwined with emotions and sensations, but they’re not emotions or sensations ― they’re a different category of feeling.
Ambiances are the different flavor of each of the four seasons. They’re the distinct character of day-to-day life in each of the different places you’ve lived, and even the different eras of your life within each place. They’re the sentimental colorings especially noticeable in childhood memories and on holidays like Halloween and Thanksgiving and Christmas and the Fourth of July, and there’s overlap between ambiance and holiday spirit. They’re the aesthetic influence you feel emanating from homes as you spend time inside them. They’re the ‘atmospheres’ of books and movies and video games, which can gently linger with you for a while even after you’ve finished reading or watching or playing. They’re the zest of travel and vacations. The ambiance of your life feels ugly or desaturated when you’re depressed. They’re often especially strong or unusual in dreams, and they’re often what cause some dreams to be especially wonderful or eerie, and the ambiance of a dream can sometimes stay with you for a little while after you wake up.
“The opacity of a rainy day rests on my soul. The world seems different, the way I ‘feel’ changes. I’m forced to retreat from the certainties of observable and definable reality in order to abandon myself to the ineffable.” 
“The way I began to look at things changed in a way that’s almost impossible to describe. It’s as if the world’s ‘personality’ had changed. Cold and rainy nights have a personality, warm and sunny spring mornings have a personality, swaying wheat on autumn hillsides have a personality.” 
“Within the lived yellow of a rose fall not only its perfume, the summer heat, the blue of the sky, but also that period of life that will not come back twice (and that was occupied by the impression we’re talking about). Within the lived yellow of a withered plant falls not only autumn as a whole, but also the uniqueness of the place and time that no autumn to come will ever present again to me.” 
“We can feel a landscape in such a way that our consciousness opens up to let the sentimental character act on us. One could define this as a ‘mood’, but it seems to me that ‘mood’ isn’t correct. Try to compare a feeling of happiness with a feeling of joyful color of consciousness, and you’ll notice a clear difference.” 
Atmospheres: Aesthetics of Emotional Spaces
[by Tonino Griffero]
“Atmospheres are something we all know. They’re something for which ‘there’s a sense’. They’re omnipresent ― though largely unacknowledged. In fact, there’s probably no situation that’s totally deprived of an atmospheric charge.”
“We say that there’s ‘something in the air’ or that we feel ‘at home’. It’s well known that the atmosphere of daytime is different from the atmosphere of night, and that to paint the walls essentially means to alter the atmosphere of the room. One can tell immediately whether a film is French or American by its overall atmosphere.”
“We feel something when visiting a given apartment for the first time, whose explanation, though ― as much as it could be partially correct ― almost always ends up sounding like a flat rationalization.”
“The question ‘What is an atmosphere?’ still hasn’t been answered satisfactorily. Of course, like emotions, atmospheres too are curious in that they lose meaning when you try to describe them ― you have to be in them to understand them.”
“Perceiving an atmosphere means grasping a feeling in the surrounding space ― sensibly, emotionally, and cognitively. It’s a ‘resonance’ of the felt space, a way in which it feels different from others. It’s a ‘something-more’, a je-ne-sais-quoi perceived in a given space, but never fully attributable to the objectual set of that space.”
“Atmospheres are indeed feelings, but mostly ‘external’ ones, effused into a space and tied to situations.”
They’re a strange mix of the objective and the subjective. Ultimately, they’re feelings, but we attribute them to things outside of ourselves, such as books, movies, homes, vacations. We can also talk about the ambiance of our life as a whole ― both at a given moment or during a given era.
“Atmospheric perception is a synaesthetic and sensorimotor unity of experience that allows one to holistically sense complex situations.”
“All phenomenological experiences are combined into a single perception.”
They strike me as the ‘most right-brained’ thing there is, as well as the ‘most subjective’ thing there is. The term ‘gestalt’ also comes to mind.
At times, they’re reminiscent of aftertastes, in that some influence or essence ― of the place you just were, or the dream you just had, or the book you were just reading, or the movie you just watched ― is still with you.
“Atmospheres ― at yet another first approximation ― are something like an experiential effect caused by the difference between places. Though, they can’t be analyzed by describing places, nor are they wholly reducible to places.”
Place has a strong (almost certainly the strongest) influence on ambiance, but you can experience vastly different ambiances in exactly the same place, depending on all the other circumstances of your life. This is especially noticeable from the way that drugs and alcohol affect the ambiance, and the way that depression affects the ambiance.
The ambiance of your life at a given time is determined by a balance of internal factors (such as the emotions you feel) and external factors (such as the city you’re in). Sometimes the internal factors play the more prominent role, and other times the external factors do.
“An atmosphere tinges everything. Much of the time, it’s comparable to goggles, which you don’t see when you look through them.”
As with everything else, we habituate to ambiances and eventually stop noticing them. Consequently, it might seem like you’re not experiencing any particular ambiance at the moment in the same way it seems like the room you’re in doesn’t smell like anything. There are actually multiple connections between ambiance and scent.
“Smell is sense mostly closely linked to memory. This is possibly due to the olfactory system’s close anatomical ties to the hippocampus, and because it’s the only sense involved in the limbic system ― areas of the brain involved in emotional and place memory.” 
“A whiff of perfume, or even the slightest scent can recreate an entire environment in the world of the imagination.”  Hearing a certain song or tasting a certain food can have a similar effect.
“It seems that one largely smells an atmosphere, breathes it in, and that therefore in scent it’s preserved. Scents are atmospheric more than any other sense phenomenon, giving a rhythm ― the morning coffee, freshly baked bread, flowers in bloom ― to everyday and seasonal life.” 
Possibly due to habituation, ambiances are often much more noticeable in hindsight. “Once the ambiance changes, you think, ‘Hmm, it’s different now,’ and then you realize what it was before.” [Pannenkoek]
“It’s hard to deny the atmospheric charge attributed to a city as an almost sacred landscape. It’s common to identify a city, and even its districts, with the atmospheric effect produced by their polysensorial image.”
“Both in life and with art, the first time is charged with an enormous yet fragile atmospheric potential. The atmosphere prototypical for us is the one suggested by the first impression. But the second (and third, fourth…) impression also gives rise to a less intense atmosphere.”
In general, the more novel the experience, the stronger the ambiance. For example, in my own life, the ambiance of the first day of school each year was always especially strong.
“Atmospheres exist in the same way as many other entities ― while being fundamental to the lived human experience, they turn out to be almost entirely superfluous from the scientific perspective.”
I couldn’t believe this phenomenon wasn’t mentioned in any book I’d ever read, even after majoring in psychology.
“As a dynamic process, the atmosphere perceived could very well change ‘valance’ and ‘color’ for various reasons. For example, it may change because of even a slight change in the surrounding space. Or because of a change in the climate, such as when a shaded space brightens up when the clouds disappear. Or due to an additional cognition, such as the discovery of the fictional or manipulative character of a situation. Or, even more simply, due to a change in physiological conditions ― when our stomachs are out of sorts, they can cast a pall over all things.”
They’re incredibly holistic and volatile. And they’re fragile in the sense that beautiful ones can easily become uglier.
“An atmosphere can overwhelm us, it can be recognized without being strongly felt, it can elicit a resistance that pushes us to change it, it may be perceived differently over the course of time.”
“A bright atmosphere isn’t simply the result of there being a large amount of light present. Rather, it’s a synaesthetic phenomenal quality resulting from a combination of optical, auditory, olfactory, gustatory, and tactile impressions, as well as those related to past memories and future possibilities.”
“Live in each season as it passes ― breathe the air, drink the drink, taste the fruit, and resign yourself to the influence of the earth.” [Henry David Thoreau]
“A spring wind brings to us with its blow the whole vastness of the world.” 
“Just as we’re always necessarily in a certain mood, we’re forever and always atmospherically involved.”
“Atmospheres are the great feelings of life.”
Every home has an ambiance ― and even individual rooms have an ambiance of their own. Every hotel has an ambiance. Every vacation has an ambiance. Every long walk and long car trip has an ambiance. Every holiday you celebrate has an ambiance. Every childhood memory has an ambiance. Every dream has an ambiance. Every film has an ambiance. Every fiction book has an ambiance ― and even non-fiction books have them too. Every song has an ambiance. Every video game has an ambiance ― and even individual levels usually have an ambiance of their own. Every painting of a place has an ambiance ― and even abstract paintings have them to some degree too.
Perhaps you could say that almost everything has an ambiance, but some things have more of an ambiance than others.
I think that when we do talk about ambiances, we often just end up using the word “mood”. What makes this confusing though is that, in psychology, moods are thought of as less specific, less intense, longer-term emotional states. And the space of emotions/moods is modeled something like these:
Ambiances exist in a different space, though. A seemingly infinite rainbow of possible ambiances can be experienced while feeling joy or sadness or any of the emotions listed. For example, take several different points in your life when you were happy, and you’ll almost certainly be experiencing different ambiances at each. And ambiances are still experienced in the absence of feeling any significant emotion.
“Ambiance and mood are connected, but they’re not the same thing.” 
Emotions and sensations are traditionally considered difficult to put into words, but however difficult they are, ambiances are even more so.
If someone were to ask you to convey to them in words the ambiance of your life at the moment, I really don’t think you can. It might at first seem like you could do it justice simply by describing your setting, but that’s not enough ― it’s influenced by all aspects of your life, so you’d have to somehow include those too. But even still, although any vivid enough description you give will evoke some ambiance in the mind of a listener, I can’t imagine it’d be identical to the one you’re experiencing ― they’re just too holistic and personal and connotative and sensitive and fragile. It’s similar to how the ambiance of a movie differs from the ambiance of the book it’s based on, or how the same is true of a movie and its remake. Ultimately, at least in practice, there are probably no words you can utter that will accurately evoke the ambiance you’re experiencing in the mind of someone else.
While it’s easy to find words to describe the setting or circumstances primarily responsible for evoking a particular ambiance, when it comes to describing the ambiance itself, I can’t help but feel that language falls short.
I think you can meaningfully describe them on spectrums from “beautiful” to “ugly”, “novel” to “familiar”, and “intense” to “faint”.
And I think you can accurately evoke an ambiance in the mind of someone else when it relates to a shared experience ― the ambiance of a movie you’ve both seen, or the ambiance your old home you both grew up in, or the ambiance of winter in a given place. But, in practice, I don’t think there’s any combination of words that’ll accurately evoke that ambiance in the mind of someone who hadn’t had that experience. In that sense, they’re more or less ineffable.
[Pannenkoek] “So in the case of books, the ambiance is constructed entirely through words. However, you say it can’t be accurately conveyed in words. Isn’t that contradictory?” Here’s how I think about it. Imagine that your friend, who hasn’t read your favorite fiction book, asks you to accurately convey to him or evoke in his mind the ambiance of that book, in words, within the space of a single sheet of paper. If you wrote out your one-page max answer to the best of your ability, and your friend then read what you’d written and then read the book itself, and then compared the ambiance of each ― he’d almost certainly say that what was conveyed/evoked by what you’d written didn’t get it right.
“The creation of an atmosphere is a special application of language, for special purposes. An ‘indescribable’ character.” [Wittgenstein]
I felt them more strongly when I was a kid. I’m not sure why, or to what degree that applies to other people. When I’d draw pictures, I’d essentially be trying to capture/convey a beautiful ambiance I was imagining. I still more or less think about art that way.
Every piece of art ― paintings, books, movies, songs ― has an ambiance. However, not every piece of art is intended to have a beautiful ambiance, and not every piece of art has creating/evoking a certain ambiance as its primary purpose.
“There was this very definite aesthetic shift from what I normally experience in the room.”i
“It’s more of an ethereal change.” 
“I didn’t have a word for ambiance before reading this. The closest I had was the feel of something.” 
“It wasn’t really alarming at first, since the change was subtle, but I did notice that my surroundings took on a different tone at certain times: the shadows of nightfall seemed more somber, my mornings were less buoyant, and walks in the woods became less zestful.”i a description of depression
“William James describes a vague ‘feeling of knowing’ that doesn’t seem to have a direct sensory or perceptual content to it. For example, have you ever walked into a particular room for the first time and just felt it to be a great place to hang out? The idea is that you’re simultaneously processing the whole room at once ― the music, the art on the walls, the furniture, the relations between the parts ― into one feeling.” 
“It’s so pervasive, but also subtle. You feel it at the back of your consciousness. It’s almost like a halfway point between ‘your mood’ and ‘the atmosphere’ (in the traditional senses of the terms) but you perceive it as this single thing.”i
“In literature, mood is defined as ‘a literary element that evokes certain feelings or vibes in a reader’, or ‘the atmosphere that a work produces in the mind of a reader’, or ‘the aura that surrounds a story’. Atmosphere and setting are connected, but they may be considered separately to a degree. Though mood is suggested through elements chosen by the author, the effect a literary work has upon the reader is subjective and produces different associations from reader to reader.”i
“In architecture and spatial design, atmosphere refers to the sensory qualities that a space emits ― an immediate form of physical perception, recognized through emotional sensibility. Architect Peter Zumthor describes architectural atmospheres as ‘this feeling of presence under whose spell I experience what I otherwise would not experience in precisely this way’.” 
“It’s like the overall feel of a video game and also your life at the time you were playing it.” [Pannenkoek]
“that nostalgic feeling when you think about a place from childhood” 
- Hans Lipps, collected by Tonio Griffero
- Ludwig Klages, collected by Tonio Griffero
- Moritz Geiger, collected by Tonio Griffero
- Philippe Fernandez
- Wikipedia’s Sense of Smell article
- Gaston Bachelard, collected by Tonio Griffero
- Gernot Böhme, collected by Tonio Griffero
- Jeremy Mann
- Polina Yakovleva
- Mikaël Aguirre
- Erwin Straus, collected by Tonio Griffero
- Leonid Afremov
- Jim Buchanan
- Siegfried Zademack
- (source lost)
- Noah Hermalin
- William Styron
- Chris Niebauer
- Vikram Iyer
- Wikipedia’s Mood (Literature) article & literartydevices.net
- Wikipedia’s Atmosphere (Architecture and Spatial Design) article
- (source lost)