Size-dependent volatility of diesel nanoparticles: chassis dynamometer experiments

We analyzed the size-dependent volatility of nanoparticles in a diameter range of 30-70 nm in diesel exhaust emissions. The test system included a medium-duty diesel truck on a chassis dynamometer, a single-stage dilution tunnel, a tandem differential mobility analyzer (TDMA) equipped with an electric furnace, and a condensation particle counter. The size shifts of monodispersed diesel nanoparticles under changing furnace temperatures were measured by TDMA in the gas phase. Together with the reduction of average particle size and volume, we observed the development of bimodal size distributions resulting from the separation between semivolatile and nonvolatile species as the furnace temperature was increased. While 91-98% of the particles were found to be semivolatile species by total volume during the idling engine condition, only 6-9% were semivolatile during the one-half engine load condition. We also found that smaller particles contained a larger fraction of semivolatile species.