Isotopic evidence for acidity-driven enhancement of sulfate formation after SO emission control.

After the 1980s, atmospheric sulfate reduction is slower than the dramatic reductions in sulfur dioxide (SO) emissions. However, a lack of observational evidence has hindered the identification of causal feedback mechanisms. Here, we report an increase in the oxygen isotopic composition of sulfate ([Formula: see text]) in a Greenland ice core, implying an enhanced role of acidity-dependent in-cloud oxidation by ozone (up to 17 to 27%) in sulfate production since the 1960s.