The two main propulsion engines on Staten Island Ferry Alice Austen (Caterpillar 3516A, 1550 hp each) were fitted with selective catalytic reduction (SCR) after treatment technology to reduce emissions of oxides of nitrogen

(NOx). After the installation of the SCR system, emissions from the ferry were characterized both pre- and post-

aftertreatment. Prior research has shown that the ferry operates in four modes, namely idle, acceleration, cruise,

and maneuvering modes. Emissions were measured for both engines (designated NY and SI) and for travel in both

directions between Manhattan and Staten Island. The emissions characterization used an analyzer system, a

data logger, and a filter-based particulate matter (PM) measurement system. The measurement of NO

x, carbon monoxide (CO), and carbon dioxide (CO2) were based on federal reference methods. With the existing control strategy for the SCR urea injection, the SCR provided approximately 64% reduction of NO x for engine NY and 36% reduction for engine SI for a complete round trip with less than 6.5 parts per million by volume (ppmv) of ammonia slip during urea injection. Average reductions during the cruise mode were 75% for engine NY and 47% for engine SI, which was operating differently than engine NY. Reductions for the cruise mode during urea injection typically exceeded 94% from both engines, but urea was injected only when the catalyst temperature reached a 300 °C threshold pre- and postcatalyst. Data analysis showed a total NO x mass emission split with 80% produced during cruise, and the remaining 20% spread across idle, acceleration, and maneuvering. Examination of continuous NOx data showed that higher reductions of NOx could be achieved on both engines by initiating the urea injection at an earlier point (lower exhaust temperature) in the acceleration and cruise modes of operation. The oxidation catalyst reduced the CO production 94% for engine NY and 82% for engine SI, although the high CO levels during acceleration did cause analyzers to over-range. No clear, quantitative conclusions could be made regarding the effects of the SCR on PM.