Ship emission variations during the COVID-19 from global and continental perspectives

The COVID-19 pandemic and the International Maritime Organization's (IMO) 2020 fuel-switching policy have profoundly impacted global maritime activities, leading to unprecedented changes in shipping emissions. This study aimed to examine the effects from different scales and investigate the underlying drivers. The big data model Ship Emission Inventory Model (SEIM) was updated and applied to analyze the spatiotemporal pattern of global ship emissions as well as the main contributors in 2019 and 2020. Overall, ships emitted NO_x, CO, HC, CO₂, and N₂O declined by 7.4 %-13.8 %, while SO₂, PM_2.5, and BC declined by 40.9 %-81.9 % in 2020 compared with 2019. The decline in CO₂ emissions indicated a comparable reduction across vessel tonnages. Ship emissions occurring at cruising status accounted for over 90 % of the ship's CO₂ emission reduction. Container ships, chemical tankers, and Ro-Ro vessels were the primary contributors to the emission reductions, with container ships alone responsible for 39.4 % of the CO₂ decrease. The ship's CO₂ emissions variations revealed the decline-rebound patterns in response to the pandemic. Asian-related routes saw emissions drop in February 2020, followed by a rebound in May, while European and American routes experienced declines starting in May, with a recovery in August. Further analysis of CO₂ emission in Exclusive Economic Zones (EEZs) showed high temporal consistency between vessel CO₂ emissions, sailing speeds, and international trade volumes across continents, and exhibited heterogeneity in main contributing ship type of emission reduction on continental scale. Our study reveals the short-term fluctuation characteristics of global ship emissions during the pandemic, particularly focusing on their spatiotemporal evolution and the inherent disparities. The results highlight the correlation between global ship emissions and trade, as well as the operational status of ships, and their rigidity.