Meta-Analysis of Marine Vessel Particulate Emission Factors for Fine-Scale Air Pollution Modeling in Port Communities

Port communities are subject to air pollution from diverse sources including on-road diesel-powered vehicles, industrial activity, and ship traffic. A 2016 review of progress and future directions in research on the human health effects of air pollution highlighted the importance of fine-scale modeling in urban areas and identified the quality of emission inventories as a significant limiting factor.[1] While emission inventories for on-road vehicles are continually improving, those for ships are still often produced via activity-based estimates that result in poor spatiotemporal resolution.[2] AIS-based modeling of ship emissions greatly improves the spatiotemporal resolution of emission inventories, but it continues to be limited by the emission factors used to convert from the speed data provided in the AIS database to an emission rate of a given contaminant. Ships move internationally and they vary widely in type, technology, and age. Early experimental studies of ship particulate emissions were more concerned with developing global emission inventories, which are dominated by ships operating at high-load, cruising conditions; however, port emissions characterized more by emissions under low-load maneuvering, loading/unloading, and idling conditions. For this meta-analysis, 54 papers with measurements of particulate emissions from ships were analyzed with the goal of developing representative emission factors for PM_2.5 under the low-load conditions characteristic of in-port maneuvering, docking, and hoteling. The papers, identified through a broad literature review, include laboratory-based test rig, onboard in-stack, and plume intercept studies. Emission factors were compiled from all the studies, converted to brake-specific units (g kWh^-1) where necessary using either measured or assumed fuel consumption rates, and analyzed to characterize the influence of engine load, fuel sulfur content, and ship/engine characteristics on emission factors. The role of fuel sulfur content is of particular interest because of the changing marine fuel regulations over the past decade. Emission factors were developed to be representative for broad classes of vessels, for distinct operating conditions occurring in or near ports, and for different fuel sulfur content regimes corresponding to the levels mandated by the IMO. Emission factors were developed for fuel sulfur contents corresponding to post-2015 Sulfur Emission Control Area (SECA) levels of less than 0.1% sulfur by mass, 2012-2015 SECA levels of less than 1%, and pre-2012 levels greater than 1%. Emission factors were further stratified by ship type because different ports have different ship fleet composition, and by the operating conditions hoteling, low-speed maneuvering, and cruising. Finally, the differences in results from laboratory, onboard in-stack, and plume intercept studies were considered.

[1] West, J.; Cohen, A.; Dentener, F.; Brunekreef, B.; Zhu, T.; Armstrong, B.; Bell, M.; Brauer, M.; Carmichael, G.; Costa, D.; Dockery, D.; Kleeman, M.; Krzyzanowski, M.; Kunzli, N.; Liousse, C.; Lung, S.; Martin, R.; Poschl, U.; Pope, C.; Roberts, J.; Russell, A.; Wiedinmyer, C., "What We Breathe Impacts Our Health: Improving Understanding of the Link between Air Pollution and Health". Environmental Science & Technology 2016, 50, (10), 4895-4904.

[2] Jalkanen, J. P.; Johansson, L.; Kukkonen, J.; Brink, A.; Kalli, J.; Stipa, T., Extension of an assessment model of ship traffic exhaust missions for particulate matter and carbon monoxide. Atmospheric Chemistry and Physics 2012, 12, (5), 2641-2659.