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Introduction of modern diesel aftertreatment, primarily selective catalytic reduction (SCR) designed to reduced NOx, has increased the presence of urea decomposition byproducts, mainly ammonia, in the aftertreatment system. This increase in ammonia has been shown to lead to particle formation in the aftertreatment system. In this study, a state of the art diesel exhaust fluid (DEF)-SCR system was investigated in order to determine the influence of DEF dosing on solid particle count. Post diesel particulate filter (DPF) particle count (> 23 nm) is shown to increase by over 400% during the World Harmonized Transient Cycle (WHTC) due to DEF dosing. This increase in tailpipe particle count warranted a detailed parametric study of DEF dosing parameters effect on tailpipe particle count. Global ammonia to NOx ratio, DEF droplet residence time, and SCR catalyst inlet temperature were found to be significant factors in post-DPF DEF based particle formation.

Diesel engines have been identified as contributing to more than half of the transport sectors black carbon (BC) emissions in the US. This large contribution to atmospheric BC concentrations has raised concern about source specific emission rates, including off-highway engines. The European Union has recently implemented more stringent particulate regulations in the form of particle number via the Particle Measurement Programme (PMP) methodology. The PMP method counts the non-volatile fraction of particulate matter (PM) above 23 nm and below 2.5 μm via a condensation particle counter. This study evaluates a surrogate black carbon method which uses the PMP particle count method with a correlation factor to the BC fraction. The transient capable Magee Scientific Aethalometer (AE-33) 880 nm wavelength channel was used to determine the BC fraction.

Light absorbing components of aerosols, often called black carbon (BC), are emitted from combustion sources and are believed to play a considerable role in direct atmospheric radiative forcing by a number of climate scientists. In addition, it has been shown that BC is associated with adverse health effects in a number of epidemiological studies. Although the optical properties (both absorbing and scattering) of combustion aerosols are needed in order to accurately assess the impact of emissions on radiative forcing, many models use radiative properties of diesel particulate matter that were determined over two decades ago. In response to concerns of the human health impacts of particulate matter (PM), regulatory bodies around the world have significantly tightened PM emission limits for diesel engines. These requirements have resulted in considerable changes in engine technology requiring updated BC measurements from modern engines equipped with aftertreatment systems.