当国家足够富裕时，就能够负担更清洁的技术、开始实施环境立法以减少室外空气污染，墨西哥城和智利的圣地亚哥现在就是如此。
When countries become sufficiently rich, they can afford cleaner technology and begin to enact environmental legislation to reduce outdoor air pollution, as we now see in Mexico City and Santiago, Chile.