As China struggles to find ways to remedy the noxious haze that lingers over Beijing and other cities in the winter, researchers from Georgia Institute of Technology have cast serious doubt on one proposed cause: high levels of ammonia in the air.
The wintertime air pollution has gained attention in the scientific community in recent years, prompting some scientists to propose that ammonia, emitted into the air from agricultural activities and automobiles, could be a precursor that strongly promotes the formation of the haze.
Georgia Tech researchers countered that theory in a study published September 21 in the journal Scientific Reports. The study was sponsored by the National Science Foundation.
“With China and other countries exploring ways to reduce air pollution, it’s important to understand the chemistry behind how that haze forms,” said Rodney Weber, a professor in Georgia Tech’s School of Earth & Atmospheric Sciences. “What we’ve found is that the atmospheric ammonia is not a large driver of those air conditions, as has been proposed.”
The researchers used advanced computer modeling to examine the chemistry of how sulfur dioxide and nitrogen oxide – two gases pumped into the atmosphere from coal-burning power plants and other fossil fuel combustion – interact to form sulfate aerosol, one major cause of the haze that can wreak havoc on human and ecosystem health.
“Typically, sulfate aerosol is produced through a chemical reaction that oxidizes sulfur dioxide to form sulfate particulates,” said Athanasios Nenes, a professor and Johnson Faculty Fellow in the School of Earth & Atmospheric Sciences and the School of Chemical & Biomolecular Engineering. “In that process, water is absorbed by the sulfate as it is produced and tends to make the particle very acidic, which shuts down certain pathways for further sulfate formation.”
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