For many years, research on health effects of PM was focused more on respiratory than on cardiovascular effects, despite the fact that in early episodes in London (1952) and the Meuse Valley (1930), many of the pollution deaths had been cardiovascular (6). In the last 15 years or so, however, much research has been devoted to cardiovascular effects, especially of PM, and this research has been both observational and experimental. As a result, there is now general consensus that PM does have serious cardiovascular effects, as evidenced from increased cardiovascular deaths after both long term and short term exposures, and from increased cardiovascular hospital admissions after high pollution days