In-use Emission Measurements from Two High-Speed Passenger Ferries Operating in California with Tier 2 and Tier 3 Marine Diesel Engines

Marine diesel engines operating in ferries and other commercial harbor craft (CHC) represent a significant fraction of near-source health risk to port and coastal communities, and emissions must be reduced to protect public health and meet federal national ambient air quality standards. In this study, we measured in-use particulate matter (PM) and gaseous emissions — including carbon monoxide (CO), carbon dioxide (CO₂), nitric oxide (NO), and nitrogen dioxide (NO₂) from two high-speed passenger ferries in the San Francisco Bay Area: one equipped with tier 2 engines with 18,096 h, the other equipped with tier 3 marine engines with 6392 h at the commencement of the study. Whereas marine engines are certified by United States (US) Environmental Protection Agency (EPA) over the ISO 8178 E3 steady-state cycle, we used portable emissions measurement systems (PEMS) to measure emissions during normal revenue service, which includes some transient and some steady-state operation. Measured real-world emissions were below relevant certification limits for CO, NOx, and PM; average in-use NOx emissions were 4.62 and 3.62 g/bhp-h for the tier 2 and tier 3 engine, respectively, CO emissions were 1.55 and 1.60 g/bhp-h for the tier 2 and tier 3 engine, respectively, and PM emissions were 0.044 g/bhp-h for the tier 3 engine. The ferry with tier 3 engines was also equipped with an aftermarket selective catalytic reduction (SCR) system designed to further reduce NOx emissions to levels below the certification level of the engine. However, due to a diesel exhaust fluid (DEF) dosing malfunction, no appreciable NOx reductions were recorded during the testing. The SCR system was designed with a platinum-group metal oxidation catalyst to reduce ammonia slip, which may have contributed to the observed 76% reduction in CO, 74% reduction in PM, and 23% increase in the NO₂/NOx ratio. Findings from this study suggest certification data are good predictors of real-world emissions from tier 2 and tier 3 marine engines and underscore the need to properly maintain and operate SCR systems.