A detailed study is undertaken to examine how 2010+ diesel engine exhaust emissions change when a soybean-derived B20 biodiesel fuel is used instead of a conventional ultra-low sulfur diesel fuel and to investigate how these changes impact the aftertreatment system. Particulate matter (PM) emissions for each fuel are characterized in terms of mass emissions, size distributions, organic versus soot fraction, metals content, and particle morphology. PM mass recorded by Dekati Mass Monitor, thermal analysis of quartz filters, and calculated from particle size distributions consistently shows a 2 - 3 fold decrease in engine-out soot emissions over a wide mid-load range when changing from ULSD to B20 fuel. This is partly due to a decrease in particle number and partly to a decrease in average size. HC and NO emissions, in contrast, exhibit little change with fuel type. "Hot" dilution sampling, consistent with exhaust conditions, was employed as opposed to regulatory methods suited for post-DPF emissions levels. Under these conditions, the particles are ~90% soot, 10% semivolatile and with little metal content from either fuel. Similar fractal-like geometries and primary particle dimensions are observed for the soot from both fuels. HC and NO aftertreatment is equally efficient for both fuels, and exhibits little influence on particle emissions. DPF loading is slower for B20 fuel, as expected from the lower soot content. The loading is non-linear for both fuels, likely due to some passive regeneration. Active DPF regeneration is achieved in 15 minutes for both fuels.