Investigation of particles emitted from modern 2-stroke scooters

Transmission electron microscopy (TEM), combined with X-ray energy dispersive spectroscopy (EDS)—both single and tandem differential mobility analyzer (TDMA)—have been used to investigate particles emitted by two modern 2-stroke scooters with different mixture preparation systems (direct injection and carburetor). In this study, we focused on investigating the influence of engine type and catalytic converter on morphology, volatility, and structure of the particles. The experiments showed an almost complete removal of the enormous number of exhaust particles when the temperature of an evaporation tube along the sampling line is increased from ambient to 400 °C. These results suggest that the exhaust particles emitted by 2-stroke scooters are volatile and no indication on the occurrence of layer structure was found, regardless of the mixture preparation system of the engine. Exhaust particles scanned before the catalytic converter were higher in number and lost a larger fraction of their volume in the evaporation tube compared to those scanned downstream of it. The presence of three major particle groups was identified by TEM analyzes, namely particles that are dominant in number but unstable under vacuum at room temperature, soot-like agglomerates and calcium-rich particles. The size of the unstable particles obtained by TEM agrees fairly with the result measured by differential mobility analyzer (DMA). We conclude that number concentration and size distribution of the particles emitted by 2-stroke scooters, are roughly in the range of 4-stroke diesel engines; however, the nature of the particles is quite different.