Why I need envirosuit on that planet?

[demiare]

Unsure that this is not technically issue, but quite possible it's not so I will post it in general forum.

After wasting a hour I finally generated a perfect bloody hell planet (hint: there is a single water source on whole planet! [:D]), but after starting actual game I found something strange.

Why we need to wear envirosuits instead of filters here (see image)? Temperature is fine too -24C...+31C.

P.S. Was anybody capable to create a planet with alien life BHL between 1 and 3? All I was able to get is either 0 (Siwa) or 4 (anything else).

[Antediluvian_Monster]

Too much sulfur dioxide will push RHL to 4/insidious. I think that's the reason why Limnos class planets will always be unbreathable, even after introduction of Earth plants and oxygen. I have also seen it on Boreas class worlds, though in their case it's only really relevant if you are going with a slushball Boreas as those can potentially support breathable atmosphere when Earth plants are introduced on the equator.

I have seen BHL 1-3 on Cerberus class, but probably same with other unconventional biospheres (though Cerberus class seems the only one aside Siwa and Medusa that regularily supports an alien biosphere without forcing it).

[HansLemurson]

I agree, filters should be just fine. According the the toxicology data I could find:
-CO2 levels are high enough to make the air feel very stuffy and stale, but not actually be toxic.
-Ammonia levels are high enough to make the place stink to high heaven, but not actually be toxic.
-SO2 levels are high enough to cause gagging and irritation, and you'd have problems breathing it long term. But a gas filter mask should be enough.

Interestingly, the SO2 and Ammonia should actually cancel each other out in the atmosphere, since they're an acid and a base.