Potential aerosol tradeoffs of vessel speed reduction for fresh ship plume composition and tracer coverage

Vessel Speed Reduction (VSR) lowers ship CO 2 emissions, but its aerosol consequences remain poorly constrained. Combining unmanned aerial vehicle (UAV) plume interception, single-particle mass spectrometry (SPMS), and population-balance inversion across 14 ship plumes, we reconstructed ultrafine and coarse modes and identified two marker gaps. Only 35.8% of the reconstructed particle-number population carried detectable V (29.5% at 4.9 versus 39.7% at 13.4 knots in a matched-vessel pair; 0–70.8% across a speed-blind manifold), showing operation-dependent marker coverage. Approximately 20% of analyzed particles met SPMS biomass-burning criteria, indicating potential false positives in ship-influenced samples. Plume-stratified analysis found 2.3–10.7-fold higher median sulfate-related ion signals in V/VO-bearing particles. Independent V–S co-location supports an association potentially arising from V-associated sulfur chemistry during exhaust cooling, pre-existing SO 3 uptake, or terminal co-deposition; laser desorption/ionization matrix effects may contribute to the contrast. In the matched-vessel case, VSR’s CO 2 benefit coincided with a carbon-rich particle shift, altered V/VO–sulfur signatures, and lower strict detectable-V coverage. This indicates a potential aerosol-composition and marker-reliability trade-off missed by bulk-mass metrics, with implications for hazard-relevant compositional indicators.