Our state-of-the art Urea Deposit Imaging Laboratory studies urea deposits and their formation and decomposition. A urea water solution is injected into an exhaust system to reduce NOX emissions. Deposit formation occurs during decomposition during transient engine operation. These solid polymers (deposits) that form on pipe walls, injectors, and SCR surfaces cause loss of NOX conversion efficiency, making the system less effective. Deposit formation in the decomposition reactor remains a significant challenge to aftertreatment system designers due to the complexity of the contributing factors such as temperature, flow rate, flow distribution, dosing rate, wall or mixer surfaces, droplet size, and number distribution.