在美国，每一美元的空气质量改善投资都能产生30美元收益，自1970年以来所投入的650亿美元共产生1.5万亿美元的总回报。
In the United States, air-quality improvements have yielded $30 for every dollar invested, for an aggregate return of $1.5 trillion on a $65 billion investment since 1970.