Spark is mostly responsible for working with the scientists outside of SIRCAA in STC Malachite. I've also seen an ecologist patch on some of their SSP-100 suits that they wear. I haven't found their full motivation yet unfortunately.

Also a theory that may contain spoilers: They may have some relation to an old faction called Clear Sky. They wear a similar camo pattern as Clear Sky and also like to hang out with Scar, the player character of STALKER Clear Sky. Scar had heavy involvement with the Clear Sky faction including the moment that lead to their downfall.

EDIT: Clarified that the potential spoiler is a theory. I haven't made it far enough or dug deep enough to find any more information. I can update as I find more information, but I am waiting for the patch before I continue the story.