Sampling and Measurement Methods for Diesel Exhaust Aerosol

Abstract

Awareness of adverse health effects of urban aerosols has increased general interest in aerosol sources. As diesel engines are one significant urban anthropogenic particle source, diesel aerosols have been under intense research during the last decades. This thesis discusses the measurement issues related to the diesel exhaust particles, focusing on the effective density measurement with ELPI-SMPS and TDMA-ELPI methods and presents some additional performance issues not discussed in the papers.

As the emergence of volatile nanoparticles in the diesel exhaust is sensitive to prevailing circumstances there is a need to properly control the dilution parameters in laboratory measurements in order to obtain repeatable and reproducible results. In addition to the dilution parameters, the effect of ambient temperature on the light duty vehicle exhaust particulate emission was studied. It was found that turbocharged diesel engines were relatively insensitive to changes in ambient temperature whereas particle emissions from naturally aspirated gasoline vehicles were significantly increased at low temperatures.

The measurement of effective density and mass of aerosol particles with DMA and impactor was studied and applied to characterisation of diesel exhaust particles. The TDMA-ELPI method was used for determination of the volatile mass of diesel exhaust particles as a function of particle size. Based on the measurement results, condensation was suggested to be the main phenomena driving volatile mass transfer to the exhaust particles. Identification of the process and the separation of volatile and solid mass may become important as some health effect studies suggest the volatile fraction to be a key component causing the biological effects of diesel exhaust particles.