Atmosphere (/ˈatməsfɪə/) - the pervading tone or mood of a place, situation, or creative work.

Not only is the plot of An Inspector Calls vital, but as it is written as a play it is important to consider the structure and stage directions along with the story. He increases the tension and increases the effect of the climax using dramatic techniques.

Priestley not only orders the events in the play, but also paces them to add tension for the audience. For example, at the beginning of Act two, the audience expects the story to move onto Gerald's confession however Priestly moves it onto a conversation with Sybil and Sheila to keep the audience engaged and curious. This makes the play also more realistic instead of a uniform order of what we expect to happen; it keeps us guessing even after the play has finished. Moreover, Priestley doesn't reveal all the information in chunks, he releases it bit by bit throughout the whole play so that there is always something new and interesting. It also allows the audience to think about each detail individually rather than just acknowledging a whole list of events that is thrown at them. Goole shows the picture of Eva one by one, which also keeps the audience curious. 
The contrast between the beginning and end scenes creates a dramatic change of mood when put side by side. At the beginning, everyone is seated round a table, but at the end people are either standing, shouting, drinking or crying. This does not create tension but is a visual contrast of the mood at the end compared to the beginning. These small details all add up to pace the story and also make it seem more realistic. 

The use of entrances and exits prove to be quite important in An Inspector Calls. The exits always have meaning or purpose later on in the play. Sheila exits the scene because she doesn't want to tell Goole her side of the story when she finds out that Eva was sacked. In contrast, Gerald exits the scene to then return and deliver the news that Goole was a fake. In addition, Goole also uses exits as a way to gain information for the audience; even if he is not present. He leaves Sheila and Gerald alone and they start talking about the affair he had with Daisy.
We could even say that the cliffhangers at the end of each act increases in intensity each time, building up tension and adds more suspense.

These factors that are not as obvious when watching/reading the play create a whole different atmosphere in comparison to a play without these dramatic techniques, therefore it was vital that Priestly took time to structure the play in the way that he did. The suspense wouldn't be as strong if he had dismissed these features.