Unraveling the long-term dynamics of black carbon and co-emitted air pollutant sources over the East China Sea.

Black carbon (BC) and co-emitted atmospheric species critically affect air quality and climate, yet long-term, source-resolved data in coastal regions remain scarce. Here, we present a three-year (2020-2022) observational study of trace gases (CO, NOx, CO2, SO2, O3) and particulate species (BC and PM2.5) over the East China Sea. Using Positive Matrix Factorization (PMF) and trajectory analysis, we resolve contributions from local, regional, and secondary sources. Local sources dominate NOx and SO2 variability, while regional sources contribute more to BC and CO2 in winter. Secondary sources contribute significantly to CO and O3 throughout the year. A machine learning model, incorporating AIS ship-tracking and meteorological data, isolates ship-emitted BC, revealing a decreasing trend of 0.066 μg m-3 yr-1, accounting for 44% of the total BC reduction. Wet scavenging rates of BC differ substantially by source, with regional BC removed approximately twice as efficiently as local BC. This integrated approach provides novel, source-specific insights into coastal BC dynamics, evaluates the effectiveness of ship emission controls, and informs management strategies for coastal air quality.