When Joe Brown went to India last summer, he was hoping to collect samples that could help answer some questions he’d been thinking about for a while. His years studying sanitation and global health had given him the idea that the open sewers and overflowing latrines common in the dense cities of the developing world could be linked with disease through an unusual mechanism: airborne transmission of pathogens.
Acidic sulfur emissions from power plants have been rapidly declining over the past decade, and the neutralizing base – ammonia – is emitted from a different source, and has not declined. This has led many atmospheric scientists to assume that the ambient sulfate particles we all breathe are becoming less acidic and therefore less toxic. But a new study shows this intuitive expectation hasn’t happened, at least not in the Southeast United States, where the remaining sulfate particles appear to be as acidic as ever.