Zeona has a thin atmosphere of sulfur dioxide and trioxide, crated by volcanic outgassing. There are traces of water vapor in the atmosphere, but over the last five centuries of observation particle counts have decreased 4%.
While not habitable by any spacefaring species, there is an abundance of native sulfur-devouring bacteria that thrives around the world's many volcanic vents. Interestingly, these bacterium bear genetic similarities to the native life of Illium, suggesting either a "panspermia" spread of microbes via asteroids, or accidental contamination of the original environment by careless spacefarers.
Note: This planet is the location for Firewalker: MSV Rosalie.
Mass Effect: Infiltrator·The Final Hours of Mass Effect 3·Galactic Codex: Essentials·Mass Effect Galaxy·Revelation·Ascension·Retribution·Redemption·Evolution
Soundtracks
Mass Effect Original Soundtrack·Mass Effect 2 Original Videogame Score [Atmospheric·Combat·Kasumi's Stolen Memory·Overlord·Lair of the Shadow Broker] ·Mass Effect 3 Original Videogame Score [Extended Cut·Citadel·Leviathan] ·Mass Effect: Andromeda - Original Soundtrack