ABSTRACT
The overall chemical composition of diesel particles from well-maintained modern engines is highly variable; however, the major constituents are always elemental carbon (EC, mainly from fuel), organic carbon (OC, mainly from lubricating oil), sulfates, and ash (mainly from lubricating oil). EC and OC are typically 80% or more of the particle mass. The OC/EC ratio generally decreases with load and is typically about one-third for highway cruise conditions. Figure 4.1 shows three weightings, number, surface, and mass of a typical diesel size distribution, and the relationships between the coarse, accumulation and nuclei modes and an alveolar plus tracheo-bronchial deposition curve [13]. The size distributions are modified versions of similar distributions published previously [35] and are representative of a diesel exhaust aerosol. The curves have a lognormal, trimodal form and the concentration in any size range is proportional to the area
under the corresponding curve in that range. Spark-ignition (SI) size distributions are similar, but have a smaller mass median diameter mainly due to fewer particles in the accumulation mode.
