Differences in particle number emissions of small fishing vessels, middle fishing vessels, and tugboats

The emissions from vessels have had a certain impact on air quality. This study characterized particle number (PN) emissions in the 0.3-10.0 μm size range from three vessel types (small fishing vessels, middle fishing vessels, and tugboats) across multiple operating states in two port areas of Hainan, China. Size-resolved PN of fuel-based emission factors (EF) were derived using a vessel-type stratified measurement framework and a carbon-balance approach with dilution correction. Across vessel types, number concentrations decreased with increasing particle size, while higher-load states (e.g., full-speed and sail) produced higher integrated PN and a greater contribution from larger size fractions across the measured size bins. Small fishing vessels exhibited the highest emission factors, with a maximum EF of 8.43×10 10 particles • (kg fuel) -1 , and a consistent load-dependent ordering (Full-speed > Sail > Idle > Anchor > Boot). Transient number spikes observed in low-load states may indicate combustion instability during mode transitions. Vessel age showed no statistically significant main effect in this data-set, highlighting the need for larger samples and further in-depth research. These results identify engine load as a primary factor associated with variability in the measured size-resolved PN emissions and provide empirical data for the 0.3-10.0 μm size range under real-world vessel states. • Small fishing vessels dominate PN, EF up to 8.43×10 10 particles·(kg fuel) -1 in 0.3-0.5 μm. • PN ranks by states: Full-speed > Sail > Idle > Anchor > Boot; higher load coarsens PN. • Tugboats: stable size spectra but highly variable PN (CV > 2.00), sensitive to transients. • Middle fishing vessels show coarse bursts >2.5 μm (CV > 6.50), vessel-specific drivers.