Currently available global inventories of nitrogen oxides (NOx) and other pollutant emissions from merchant ships are based, at least partly, on data published by international marine bunker fuel suppliers. However, the uncertainty of such data seems to be quite high, because the figures released by bunker fuel companies might be incomplete or based, for example, on data collected from only the largest ports. Besides, all similar other studies conducted so far were based on simplified average emission and fuel consumption characteristics of diesel engines and did not take into account variations with engine type, size, engine load and engine speed, as well as only being valid for new state-of-the-art diesel engines as supplied by the industry today. Furthermore, fuel consumption rates of the auxiliary engine equipment onboard vessels were neglected. The author therefore adopted a different approach by calculating the actual bunker amount and the fleet’s 2001 NOx emissions in order to reduce uncertainty in existing inventories and to assist in achieving a better modeling of the effects of ships’ pollutants on atmospheric chemistry. For this study, all ships of 100 gross tonnage (gt) and above were taken into account. This methodology resulted in a significantly higher world fleet fuel consumption, and, consequently, much higher oceangoing ships’ NOx emissions than known or anticipated so far. In spite of the fleet’s high NOx emission rate in absolute figures this paper shows, that when emissions are based on the annual seaborne trade, merchant shipping is an environmentally efficient mode of transportation of freight.

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