But two U. s. researchers, a transportation expert and an atmospheric scientist, decided the time had come to apply blue-sky thinking to one of the world's greatest challenges.

但是来自美国的两位研究员，一位是交通专家，另一位是大气科学家，他们认为把蓝天思考纳入世界诸多重大挑战之一时候来到了。