Black Carbon Emissions from In-Use Harbor Craft in Southern California

Abstract:

Black carbon (BC) emitted from diesel fuel combustion contributes significantly to total particulate matter emissions that impact air quality and human health. Off-road sources of BC, such as harbor craft (e.g., tugboats, passenger boats, and fishing vessels), are becoming increasingly important as emissions from on-road vehicles continue to decrease. This study characterizes BC emissions from in-use harbor craft since these marine vessels spend most of their time operating near the coast, contributing to local air pollution.

BC emission factors (EF) from a large sample of in-use vessels were measured from shore in the San Pedro Port Complex using the plume capture method. BC concentrations were measured using a custom built aethalometer and CO₂ was measured using a LI-COR LI-840a CO₂ analyzer. Onshore measurements yielded 78 emission factors from ~45 unique vessels, with passenger boats having the highest geometric mean BC EF (0.54 ± 0.81 g BC/kg-fuel). Tugboats had slightly higher BC EFs while moving with loads relative to without loads (0.66 ± 0.28 and 0.45 ± 0.68 g/kg, respectively). BC EFs for vessels under non-idle conditions were skewed, with the dirtiest 20% of plume intercepts contributing ~47% of BC emissions. Additional measurements were made onboard a passenger boat and fishing boat during typical operating conditions using the same instrumentation outlined above. BC EFs from onboard measurements were approximately normally distributed and influenced by operating mode variability. To contextualize our findings, one year of vessel traffic data were analyzed to better understand the spatial and operational variability of harbor craft and large ocean-going vessels in Southern California. Tugboats spent more non-idle operating time within 3 nm of California’s coast than all large ocean-going vessels. Moreover, the Southern California tugboat fleet is composed of few unique vessels, indicating that these marine vessels could be worthwhile targets for regulatory action.