Angel Hsu, an expert on China’s environment at the Yale School of Forestry and Environmental Studies, said Chinese officials severely restricted research into the relationship between air pollution and public health until 2013, when public pressure to confront the issue became too great to ignore. "I think the fact that people from foreign institutions are now able to do these kinds of studies is significant," she said. "[Officials] were trying not to be specific about the health implications of unfettered growth for such a long time."