Dynamic NOx emission factors for main engines of bulk carriers

•The speed was modified by eliminating influences of wind, wave and current.•The modified speed could accurately estimate main engine loads.•The dynamic emission factors of NOx were developed. Emission factors are essential for estimating ship emissions. To improve the accuracy of the nitrogen oxides (NOx) emissions, dynamic emission factors of NOx were implemented in this study. First of all, the influences of wind, waves and currents on the speed of the Automatic Identification System (AIS) were eliminated. Furthermore, with the adaption of modified speed, the accuracy of estimated main engine loads was increased, compared with the raw AIS speed. Moreover, the dynamic emission factors of NOx were further developed using modified speed for the estimation of main engine loads. In the numerical study, the dynamic emission factors of NOx model manifested an improvement of up to 86% for the estimation of the NOx emissions of two bulk carriers, compared with commonly used emission factors of NOx.