The USG program with the highest benefit-cost ratio?

I am talking here about individual, discrete activities of the government, not general or overall functions.  How about this for a nomination, namely US Embassy air quality tweets?:

Over 4 million premature deaths per year are attributed to air pollution, most of which are in low- and middle-income countries where residents do not have access to reliable information on air quality. We evaluate a large-scale program that provided real-time air-quality updates at over 40 US diplomatic sites around the world with poor preexisting monitoring. We find that the embassy monitoring program led to substantial reductions in fine particulate concentration levels, resulting in substantial decreases in the premature mortality risk faced by the over 300 million people living in cities home to a US embassy monitor. Our research indicates that monitoring and information interventions that draw attention to poor air quality in developing countries can generate substantial benefits.

Did you take these benefits into account last time you were bitching about Twitter?  Probably not.

Via the excellent Kevin Lewis.