Are we understanding the respiratory effects of traffic related airborne particles?

There is convincing scientific evidence showing that ambient particulate matter (PM) is related to both short and long term health effects. Increased mortality and hospitalisation for cardiopulmonary causes have been noted in several studies evaluating the effects of PM10 or PM2.5 (PM <10 or 2.5 μm in diameter).1 However, urban air pollution consists of a complex mixture of gases and particulate agents that vary over time and through space, depending on its sources, distance and meteorological conditions.2 Much of the scientific interest has been devoted to the toxicology of the ultrafine fraction of airborne particles (<0.1 μm).3 These particles are usually emitted from combustion sources (eg, gasoline or diesel powered engines) or are formed from chemical conversion of gases in the atmosphere. They are relatively short lived and combine into larger particles between 0.1 and about 1 μm in diameter (accumulation mode). These particles tend to penetrate deeper in the alveolar part of the lung and have a larger surface area than larger sized particles, eliciting greater potential interaction with human tissues and a stronger inflammatory reaction. The epidemiological evidence linking ultrafine particles with respiratory health effects is still limited and controversial. In the current issue of Thorax , Halonen and colleagues4 provide new and compelling evidence on the respiratory effects of particles of various sizes that will certainly stimulate further research (see page 635) . Different sized particles were measured daily in Helsinki over a period of 7 years, and a source apportionment method was applied to separate the PM2.5 fraction from four sources (traffic, long range transport, soil and road dust, and coal/oil combustion). …