Human rights groups and United Nations researchers called it “black rain.” The surprise joint U.S.-Israeli airstrikes on Iranian oil facilities last March propelled toxic and highly acidic clouds of soot and aerosolized oil into the region’s cloud cover in the wake of the attacks, casting a literal black pall across the land.

Experts with the U.N.’s World Health Organization urged Tehran’s roughly 10 million citizens to stay indoors and wear masks following Israel’s particularly devastating strike against three fuel depots and the Tehran Oil Refinery just outside the nation’s capital on the night of March 7. Medical professionals understood almost immediately the potential risk for lung damage and skin burns following the bombing.…