In-use gaseous and particulate matter (PM) emissions were characterized aboard a tugboat fueled with a California Air Resources Board (CARB)-based ultralow-sulfur diesel (ULSD) before and after selective catalytic reduction (SCR)-diesel particulate filter (DPF) control technologies. Emissions of measured individual gaseous pollutants include nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CO2), and ammonia (NH3) slip, while PM emission measurements include PM2.5 mass, elemental carbon (EC), and organic carbon (OC). Measurements were conducted according to the ISO 8178 measurement and sampling protocol, while emissions were weighted according to the ISO 8178-4-E3 steady-state test cycle for main engine marine applications. Overall weighted emission factors showed that the SCR reduced NOx by similar to 92%, while the DPF reduced PM2.5 emissions by similar to 96%. The lowest reductions in NOx and highest NH3 slip were observed at the 27% load point, where the exhaust temperature was below the light-off temperature of the SCR catalyst. Reductions in PM2.5 were consistent throughout all load points ranging from 92 to 97%, respectively. PM2.5 was composed mainly of OC with OC/total carbon (TC) ratios ranging from 0.85 to 0.97 before the catalyst and from 0.98 to 1.0 after the catalyst. The increasing emissions from a forced DPF regeneration were also captured in real time and are reported herein.