The chemical composition of the plumes of seagoing ships was measured during a two week long measurement campaign in the port of Rotterdam, Hoek van Holland The Netherlands, in September 2009. Altogether, 497 ships were monitored and a statistical evaluation of emission factors (g kg⁻¹ fuel) was provided. The concerned main atmospheric components were SO₂, NO₂, NO_x and the aerosol particle number. In addition, the elemental and water-soluble ionic composition of the emitted particulate matter was determined. Emission factors were expressed as a function of ship type, power and crankshaft rotational speed. The average SO₂ emission factor was found to be roughly half of what is allowed in sulphur emission control areas (16 vs. 30 g kg⁻¹ fuel), and exceedances of this limit were rarely registered. A significant linear relationship was observed between the SO₂ and particle number emission factors. The intercept of the regression line, 4.8 × 10¹⁵ (kg fuel)⁻¹, gives the average number of particles formed during the burning of 1 kg zero sulphur content fuel, while the slope, 2 × 10¹⁸, provides the average number of particles formed with 1 kg sulphur burnt with the fuel. Water-soluble ionic composition analysis of the aerosol samples from the plumes showed that ~144 g of particulate sulphate was emitted from 1 kg sulphur burnt with the fuel. The mass median diameter of sulphate particles estimated from the measurements was ~42 nm.