Characterization of structure of single particles from various automobile engines under steady-state conditions

<p>The effective density ρ_<i>eff</i> of particles emitted from various types of automobile engines was measured using a differential mobility analyzer (DMA)–aerosol particle mass analyzer method, and their morphology was investigated via transmission electron microscopy analysis. The measured exhaust particles were particles emitted from diesel engines (DEs), gasoline direct injection spark ignition (DISI) engines, gasoline port fuel injection (PFI) engines, and liquefied petroleum gas (LPG) engines. ρ_<i>eff</i> and the morphology of the particles were measured after classification with the DMA, and six electrical mobility diameters <i>D</i>_<i>m</i> ranging from 30 to 300 nm were selected. ρ_<i>eff</i> was found to decrease as <i>D</i>_<i>m</i> increased for all particles. A morphological study showed that DE and DISI particles were mainly agglomerates and PFI and LPG particles were mainly nonagglomerates. Numbers and diameters of the primary particles in the agglomerates showed no systematic differences between DE and DISI particles at a given <i>D</i>_<i>m</i>. Rather, the primary particle diameter <i>d</i>_<i>p</i> increased with increasing <i>D</i>_<i>m</i> of the agglomerates; the empirical relationship between the two diameters was found to be <i>d</i>_<i>p</i> = 8.498ln(<i>D</i>_<i>m</i>) – 12.781 for DE and DISI particles. The core (elemental carbon) diameters in the primary particles of the DE particles increased as <i>D</i>_<i>m</i> increased and were estimated to range from 8.5 nm for <i>D</i>_<i>m</i> = 70 nm to 22.1 nm for <i>D</i>_<i>m</i> = 300 nm. Although the primary particle diameter and core diameter depend on <i>D</i>_<i>m</i>, the organic coating (shell) thickness, which ranged from 5.1 to 7.4 nm, was found to be independent of <i>D</i>_<i>m</i>.</p> <p>Copyright © 2016 American Association for Aerosol Research