Env_fog_controller
How to add fog to your map
Step 1:
Use the entity tool and write envfogcontroller in the right navigation. Place this entity anywhere on the map.

Step 2:
Double click envfogcontroller in camera view, right click in 2D, view or click ALT + ENTER.
Step 3:
Now we have to change some settings. Find Fog Enable and set it to Yes.

You are done now!But there are some settings you can change to make it look better.
Other settings:
Fog Max Density That is the Density of the fog. Use some thing between 0 and 1. On my upcomming map (awp_forestlake) I am useing 0.3! 1 is default.
Fog Start We can change how far away you can see it. So find Fog Start, and set it's value to 0.0. It is better when it is closer. Default is 500.0.
Fog End Now find Fog End, and set it's value to 2000.0. 2000.0 is default. But it's best when Fog End is a couple of thousands.
Primary Fog Color You can change that to any color you want but it is best with the white-grey color.
Secondary Fog Color The same here but make the color slightly different.







