A common bug in the current version of SiN Episodes: Emergence causes a stark mismatch between how fog is rendered over the game world vs individual props, which can be very immersion breaking.

This is caused by a glitch related to how current versions of DirectX 9 renders this branch of the source engine. From what I gathered on PC Gaming Wiki[www.pcgamingwiki.com], Nvidia technically fixed this back in 2007, however the fix only applied to games that had a current version of a Source Engine branch. SiN had not had an engine update after it launched, and thus the fix doesn't apply.

As of right now, unless you have access to a PC that does not use either a Nvidia or AMD card, there is no perfect solution to this without some kind of an engine update. But here is a temporary solution:

We're going to completely disable fog so the discrepancy does not appear.

Again, this is not an ideal solution, as it does remove some of the atmosphere from these levels. Also bear in mind that this also does not fix a similar issue that occurs when underwater. But in the absence of an actual fix, this is still better than nothing.

Open your console with the "~" key (you may need to enable it via the advanced settings in the options)

After starting a new game, type in the following commands:
sv_cheats 1
fog_override 1
fog_enable 0
fog_enableskybox 0

And that's it. There might be a scripted sequence or two that re-enables fog automatically, in which case just do this again. These settings are maintained upon saving and reloading as well, so you mercifully don't have to do this every time you load your game.