Which preposition to use with unsmudged

by Occurrences 1%

Below him lay the level tundra, merging indistinguishably with the white anchor-ice of Behring Sea; beyond that a long black streak of open water, underscoring the sky as if to emphasize the significance of that empty horizon, a horizon which for many months would remain unsmudged by smoke.

Which preposition to use with  unsmudged