Annual changes of ship emissions around China under gradually promoted control policies from 2016 to 2019

Abstract. Ship emissions and coastal air pollutions around China are expected to be alleviated with the gradually implemented of domestic ship emission control (DECA) policy. However, there is so far a lack of a comprehensive post assessment on the ship emission response after the policy implementation. This study developed a series of high spatiotemporal ship emission inventories of China’s inland rivers and the 200 Nm zone from 2016 to 2019 based on an updated Ship Emission Inventory Model (SEIM v2.0) and analysed the interannual changes of emissions under the influence of both ship activity increase and gradually promoted policy. The route restoration technology in SEIM v2.0 has greatly improved the spatial distribution of ship emissions and the river vessels (RVs) are better distinguished by using the spatial frequency distribution method. From 2016 to 2019, SO2 and PM emissions from ships decreased by 29.6 % and 26.4 %, respectively, while ship NOX emissions increased by 13.0 %. Although the DECA 1.0 policy has been implemented since 2017, it was not until 2019 with the DECA 2.0 that significant emission reduction was achieved, e.g., 33.3 % regarding SO2. Considering the potential emissions brought by continuous growth of maritime trade, however, an even larger emission reduction effect of 39.8 % was achieved in 2019 compared with the scenario without switching cleaner fuel. Although ocean-going vessels (OGVs) contributed to approximately 2/3 of ship emissions in Chinese waters, 2/3 of them came from ships registered in other countries. Containers and bulk carriers are still the dominate contributors to ship emissions, and newly-built, large ships and ships using clean fuel oil are taking an increasingly large proportion in emission structure. The four-year consecutive daily ship emissions were presented for major ports, which timely reflects the response of step-by-step DECA policy on emissions and may provide useful references for port observation experiments and local policy making. In addition, the spatial distribution shows that a number of ships detoured outside the scope of DECA 2.0 in 2019 to save the cost on more expensive low sulphur oil, increasing emissions in farther maritime areas. The multi-year ship emission inventory provide high-quality datasets for air quality and dispersion modellings, as well as verifications for in-situ observation experiments, which may also guide further ship emission control direction in China.