While it refers to the things that surround the scene, it has much more to do with the characters that with the scenario. The atmosphere’s aim is to give us the emotional frame of the scene. It is achieved with a deliberately intentional description, involving only aspects that, as writers, we are interested that the reader knows thus leaving out anything that interferes.
An atmosphere can’t be created without descriptions, but you don’t require many paragraphs to create it: a few lines showing the most important things are enough. The atmosphere is a usual ally in creating a specific mood. A day with a glorious sun calls for positivism and joy, while rain is always sad and melancholic.
There are some points to take into account to connect with the reader in order for him to receive what we’re communicating in a description.
Be specific. It’s not a good idea to add extra frills or beat around the bush reducing the possibility of the message being clear to the receiver. You can use poetic language, of course, but aim to reach the goal of communicating the emotions your story needs without tiring or confusing the reader.
Avoid clichés. All of these phrases have a negative effect on the reader and in reality don’t describe a scene the way you want it to be: unique and different. Paragraphs full of platitudes convey very little effort in the creation and make the text seem very similar to many others.
Don’t base yourself in appearances. This tends to disappoint, we all know that. While each place tends to be a certain and determined way, try to make your version of the scenarios a little bit different and original. Unlike the movies, literature has a lot of more weapons to accomplish an astounding description, metaphors, meaningful words, grammatical resources, similes, rhythms, musicality, etc.