PM2.5s and life expectancy
PM2.5s are particles that are small enough to enter the lungs. Particles that are larger than 3 microns in diameter (PM3s) are too large to get into the lungs.
Harvard School of Public Health found that for every reduction of one microgram per cubic metre in average levels of industrial PM2.5 emissions, there were 3% fewer deaths. The largest drops in mortality rates were in cities with the greatest reduction in fine particulate air pollution, ie PM2.5s.
Unlike the USA and many other countries, the UK do not measure PM2.5s, preferring to measure PM10s.
Source: Harvard School of Public Health press release, 15 March 2006 (archived copy).