Changes in the impacts of ship emissions on PM_2.5 and its components in China under the staged fuel oil policies

Abstract. The issue of air pollution caused by ship emissions is becoming prominent with the increasing global shipping activities. China has carried out staged fuel oil policies in the past few years to meet the requirements of the global low sulfur regulation by the International Marine Organization (IMO), called the IMO Regulation. However, the impacts of ship emissions on air quality in China after 2020 are not sufficiently understood. This study firstly updated the ship emission inventory including PM_2.5 components based on field and on-board measurements under the staged fuel oil policies. Then, the impacts of ship emissions on PM_2.5 as well as its gas precursors and primary and secondary components in China from 2017 to 2021 have been revealed by using the Weather Research and Forecasting (WRF) model and the Community Multi-scale Air Quality (CMAQ) model. We found that ship emissions increased the PM_2.5 concentrations up to 3.8 μg m^-3 in 2017 and 2.6 μg m^-3 in 2021 along China’s coastal area. The areas with high concentration levels widely distributed over the offshore waters in 2017, and shrunk to some parts of China’s coast in 2021. The contributions of ship emissions to the PM_2.5 concentrations over China’s main port cities ranged from 3.0 % to 17.4 % in 2017 and 2.5 % to 10.3 % in 2021. Our findings suggest that it is important to consider both transport pathways and formation mechanisms of secondary aerosols to combat the PM_2.5 pollution caused by shipping in different regions.