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Maritime transport has been playing a decisive role in global trade.Its contribution to the air pollution of the sea and coastal areas has been widely recognized.The air pollutant emission inventories of several harbors in China have already been established.However,the emission factors of local ships have not been addressed comprehensively,and thus are lacking from the emission inventories.In this study,on-board emission tests of eight diesel-powered offshore fishing ships were conducted near the coastal region of the north Yellow Bo Sea fishing ground of Dalian,China.Results show that large amounts of fine particles (＜0.5 μm,90％) were found in maneuvering mode,which were about five times higher than those during cruise mode.Emission rates as well as emission factors based on both distance and fuel were determined during the cruise and maneuvering modes (including departure and arrival).Average emission rates and distance-based emission factors of CO,HC and PM were much higher during the maneuvering mode as compared with the cruise mode.However,the average emission rate of Nitrous Oxide (NOx) was higher during the cruise mode as compared with the maneuvering modes.On the contrary,the average distance-based emission factors of NOx were lower during the cruise mode relative to the maneuvering mode due to the low sailing speed of the latter.