Here are some synonyms for "atmosphere," depending on the context:

General:

* Air

* Environment

* Ambiance

* Aura

* Mood

* Feeling

* Climate

* Conditions

Specific to the Earth's atmosphere:

* Airspace

* Stratosphere

* Troposphere

* Mesosphere

* Exosphere

Figurative:

* Vibrancy

* Buzz

* Tension

* Excitement

* Intimacy

In the context of a play or movie:

* Setting

* Stage

In the context of a business or organization:

* Culture

* Work environment

* Workplace

The best synonym to use will depend on the specific context in which you are using the word "atmosphere."