Ice core data show why air pollution is dropping more slowly in US and Western Europe despite lower sulfur emissions
The air in the United States and Western Europe is much cleaner than even a decade ago. Low-sulfur gasoline standards and regulations on power plants have successfully cut sulfate concentrations in the air, reducing the fine particulate matter that harms human health and cleaning up the environmental hazard of acid rain.
Despite these successes, sulfate levels in the atmosphere have declined more slowly than sulfur dioxide emissions, especially in wintertime. This unexpected phenomenon suggests sulfur dioxide emission reductions are less efficient than expected for cutting sulfate aerosols.