Spatial response of harbor craft emissions to tugboat electrification: a 3-year activity-based assessment in the...

Harbor craft are significant contributors to air pollution in port areas due to their high engine loads and frequent maneuvering operations. This study develops a high-resolution emission inventory for five commercial harbor vessels operating in the Port of Iskenderun from 2022 to 2024 and evaluates the emission reduction potential of phased tugboat electrification. Using a bottom-up activity-based approach, emissions of NOₓ, CO₂, SO₂, and PM were calculated from vessel-specific engine characteristics, operational records, and load-dependent emission factors. The results show that tugboats are the dominant emission sources, accounting for the majority of port-wide pollutant loads, while pilot and supply vessels contribute substantially less. Spatial scenario modeling reveals that emission reductions do not scale linearly with electrification level. The area achieving ≥ 50% emission reduction increased from near-zero under 25% electrification to ~ 8.8 km² at 50% and ~ 13.9 km² at 75%, indicating a threshold-like spatial expansion of air quality benefits. Full electrification of tugboat propulsion and onboard auxiliary systems would eliminate direct exhaust emissions from electrified tugboats at the point of use, avoiding more than 20,000 tons of CO₂ and several hundred tons of NOₓ, SO₂, and PM over 3 years. These findings identify tugboat electrification as a high-leverage mitigation strategy and highlight 75% adoption as a critical threshold for achieving meaningful port-wide air quality improvement.