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When acidic materials are spilled, the clean-up procedure involves adding a base chemical to neutralize the acid. Up to a point, the more base added, the more neutral and less toxic the spill becomes. Something very similar is happening in the atmosphere. 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. [Source: Georgia Tech]
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