N. Engl. J. Med. 360, 376–386 (2009)

Dirty air really can shorten your life. A drop of just 10 micrograms per cubic metre in the concentration of airborne particulate matter less than 2.5 micrometres in diameter extends human life by an average of almost 7.5 months, according to a team led by Arden Pope of Brigham Young University in Provo, Utah.

Comparing data from surveys carried out in 1979–1983 and 1999–2000, the researchers charted improvements in pollution levels in 51 US cities. They then correlated that data with changes in life expectancy over the same period, using census and health survey data to factor out other variables such as population density, income and smoking.