When drawing or painting landscapes, the atmosphere has an effect on the way we see objects.

If an object is close to the observer, there are not many (relatively) atmosphere particles between it and the observer, and therefore the object looks clear and in focus.

When an object is far away from the observer, there are many atmosphere particles between it and the observer, which scatter light, and change the way the object is seen.

Some effects to pay attention to:

Brightness values

The farther an object is, the lighter it becomes.

Color

The farther an object is, the more its color shifts toward the sky color (on a clear day, when the sky is blue, far objects will shift toward blue).

Contrast & Details

The farther an object is, it will have less contrast and details. Gradually becoming one or few brightness values.
The lightest and darkest values are in objects close to the observer (in the foreground).

Edges

Objects in the background (far) have soft edges, and look blurry.
Foreground objects look sharp, and have sharp edges.
(Look how soft the mountains are, compared to the boat).

Saturation

Far objects have dull, grayish colors, while close objects have rich colors (not too saturated though, nature is not that saturated. Too much saturation will look cartoonish).

This is part of my guide on linear and atmospheric perspective, which you can find here:
https://ranartblog.com/blogarticle19.html

Artistic License

You can use atmospheric perspective for foreground objects too, a bit like the effect of a camera.
In the next example, even though the birds are close to each other, I made the far bird with less contrast and details, lighter, and with soft edges, to create more depth in the drawing:

Even for the same object, you can use this effect.
In the next example, I made the back part of the bee less sharp, lighter, with fewer details, and with soft edges:

I hope you enjoyed.
If you have questions, I will be more than happy to answer.

Ran

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