Determining black carbon emissions and activity from in-use harbor craft in Southern California

Black carbon (BC) emitted from diesel fuel combustion contributes significantly to particulate matter emissions that impact air quality and human health. Off-road sources of BC are increasingly important as emissions from on-road vehicles continue to decrease. This study characterizes harbor craft emissions and activity, including tugboats, passenger boats, and fishing vessels. Vessel traffic data suggest that the Southern California tugboat fleet is composed of relatively few unique vessels, yet tugboats spent more non-idle operating time within 3 nautical miles of California's coast than all other vessel types (including large ocean-going vessels). Fuel-based BC emission factors (EFBC) were measured from shore in the San Pedro Bay Port Complex in Los Angeles using the plume capture method, yielding 78 EFBC values from ~45 unique vessels. Passenger boats had the highest geometric mean EFBC (0.56 ± 0.86 g/kg). Tugboats had higher EFBC while moving with versus without loads (0.64 ± 0.29 and 0.48 ± 0.67 g/kg, respectively). Non-idle EFBC for vessels were skewed, with the dirtiest 20% of plume intercepts contributing ~47% of BC emissions. Given the trends observed in both vessel activity and EFBC values, tugboats could be worthwhile targets for emissions reductions.