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# emissionDuration

The duration, in seconds, over which the system spawns new particles. Animatable.

```
var emissionDuration: CGFloat { get set }
```

## Discussion

The [`birthRate`](/documentation/SceneKit/SCNParticleSystem/birthRate) property determines the number of particles spawned during this duration. You can randomize the duration with the [`emissionDurationVariation`](/documentation/SceneKit/SCNParticleSystem/emissionDurationVariation) property.

A duration of `0.0` specifies that all particles (the value of the [`birthRate`](/documentation/SceneKit/SCNParticleSystem/birthRate) property) spawn instantaneously. Use this duration to create randomized static effects in your scene. For example, by combining this option with the [`birthLocation`](/documentation/SceneKit/SCNParticleSystem/birthLocation) and [`imageSequenceInitialFrameVariation`](/documentation/SceneKit/SCNParticleSystem/imageSequenceInitialFrameVariation) properties, you can cover a plane with a variety of sprites, creating the appearance of a grassy field.

The default value is `1.0` seconds.

You can animate changes to this property’s value. See [Animating SceneKit Content](/documentation/SceneKit/animating-scenekit-content).

---

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