Impacts of Ship Emissions on Regional Air Quality in the Post-DECA Era: A Case Study of the Yangtze River Basin.

Abstract

Under the ongoing implementation of China's Domestic Emission Control Area (DECA) policy, shipping emissions and their impacts on air quality have drawn increasing attention. However, most studies have focused on the early and intermediate phases of DECA implementation, leaving the emission characteristics and multi-pollutant responses in the post-DECA era insufficiently quantified. This study investigates the Yangtze River Basin, the world's busiest inland shipping corridor, by constructing a high-resolution emission inventory for 18,478 vessels based on approximately 230 million Automatic Identification System (AIS) trajectories in 2023, and coupling it with the WRF-Chem model to quantify the contribution of ship emissions to regional air quality. Results show that SO2 and PM2.5 emissions from Yangtze shipping have been substantially controlled in the post-DECA era, whereas NOx emissions reached 156.41 kt yr-1, accounting for 82.0% of the total emissions of major pollutants, and formed pronounced hotspots along heavily trafficked reaches, including Yichang-Jingzhou, Wuhan, and Nanjing-Shanghai. Concentration simulations indicate a stable positive contribution of ship emissions to NO2 with marked near-source effects, yielding annual mean contributions of 0.16-3.41 μg m-3 across 11 mainstem cities. PM2.5 increments are generally low, but nitrate constitutes a substantial fraction. O3 responds differently, showing clear seasonal variation driven by photochemical processes: it decreases in January and October due to near-source NO titration but increases in July under strong photochemical conditions. These findings suggest that, beyond sustaining fuel-sulfur control and particulate mitigation, inland shipping emission management should advance toward coordinated strategies centered on source-level NOx reduction.