atmospheric… I have no idea what does that means.
Atmosphere means pertaining to the air, correct, and this is the only meaning you're familiar with. So yes, comics are susceptible to atmospheric degradation, heat, damp, etc.
The other meaning of atmosphere, the one you struggle with, is best learned if you imagine a situation where there is 'just something in the air', but that this something does not relate to weather or temperature but instead relates to our imagintion interpreting it's surroundings, to which there are many examples.
The most common example would be something like love. To which one's perception of one's environment radically changes when one is in love. Everything seems prettier, everyone seems nicer, everything in the world just feels
right. I can't imagine you don't understand this perception as it's one of the most well known examples of "something in the air":
In effect, love has changed the atmosphere for you, you're imagination of your surrounding space. Ergo, if you are in a room full of love it will have different atmospherics than if you were in a room full of angry people who were staring at you.
And the second most common atmospheric situation is indeed one of threat. Imagine sitting in your room in the dark, no-one else in the house. The atmosphere is one of quiet tranquility, a peacefull atmosphere shapes your perception of your surrounding space. Now imagine you hear the sound of breaking glass in another room. You're sense of atmosphere has instantly changed, your immediate space is now dominated by a sense of dread, trepidation and nervous energy which shapes your perception of the space around you. Your once warm, cosy, soft space now feels sharp, claustrophobic and oppressive.
Another common example is the socially uncomfortable notion of awkwardness. You know how you can be having a perfectly fine conversation with someone one minute, only for the situation to suddenly change upon the utterence of one single sentence which immediately sends others into a state of awkwardness. That awkwardness is purely "in the air" and though does not exist physically can be "felt" by the people in the room, ergo: it changes the "atmosphere".
In terms of art and media, atmospherics are defined as the products ability to communicate such states of mind regarding the space you are in:
Does the scene convey the sense of grime and stink when walking through a sewer?
Does the scene convey the sense of love when there is a romantic plotline?
Does the scene convey a sense of threat if it is a thriller?
Does the scene
feel like it's set in the post-apocalypse, or does it just seem like characters are standing in a convoluted environment?
The first component of atmospherics is usually lighting:
So in the above picture, which of the three would make someone feel that their surrouning space was warm and cosy, and which would make their surrounding space feel colder and lonelier?
Then you move onto furniture: would the room feel cosier with some nice paintings on the wall and does the room feel colder with bare walls? Of course:
Then you move onto sound:
etc, etc until you've covered every aspect of artistic magic, all of which combines to create the exact atmosphere you were hoping to convey: the sense of perception of your surrounding space.