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.