The interest in ammonia (NH3) is on the rise to be used in compression ignition engines by replacing heavy hydrocarbons such as heavy oil and diesel in applications such as marine shipping in effort to reduce their carbon footprint. Diesel could be partially replaced with NH3 in the engine to reduce CO2 emissions, however a minimum percentage of diesel is required to sustain the NH3 ignition and combustion in the engine. The objective of this work is to study the impact of NH3 on the formation of soot in a dual fuel diesel engine by analyzing the exhaust soot mass concentration, morphology, nanostructure and composition, shedding more light on the chemical interactions of NH3 with diesel soot. For the engine operating at 0%, 20%, and 40% NH3 to diesel, a linear reduction in soot mass concentration and size and number of the soot primary particles is found as the percentage of NH3 increases. The soot nanostructure is investigated using Raman analysis of the solid soot particles which shows higher levels of soot graphitization with higher sp2 hybridization of the carbon atoms. Analysis of XPS spectra is done to obtain the atomic percentage of nitrogen bound to the soot surface which shows a substantial increase in the amount of nitrogen detected on the soot surface. The effect of NH3 addition on the nanostructure could be linked to the NH3 reactions with the soot surface at the active sites which limits the ability of the carbon to bind to the soot surface, suppresses soot growth. and increases the nitrogen content of the soot formed.