Contribution of Ship Emissions to Aerosol Number Concentrations: Parameterization of Plume-Scale Nonlinear Microphysics and Application

Abstract

Ships are an important source of tiny atmospheric particles over oceans capable of affecting clouds, and the change of ship fuel sulfur has been suggested to reduce particle cooling effects. Number concentrations and sizes of emitted particles are critical for assessing the climate and health impacts of shipping emissions. Here, we build the direct ship particle number (SPN) emission inventory and further propose a computationally efficient approach (look-up table, EIPN) to estimate particle number emission by accounting for the subgrid process of ship plumes. In the Yangtze River Delta (YRD) coastal area along East China Sea, the total ship particle number emission estimated based on EIPN is 7.3 × 10²³ particles with the values of 5.9 × 10²⁴ particles predicted by the SPN, showing a notable overestimation by a factor of ∼8 (compared to EIPN). The particle number and cloud condensation nuclei (CCN) under 0.4% water supersaturation (CCN0.4) conducted utilizing the EIPN with normalized mean biases (NMB) of −13.1% and −28.6% exhibit higher concordance with observations than those using the conventional mass emission inventory (NMB = −37.7%, −44.9%) and SPN (NMB = −57.4%, −72.2%), demonstrating the significant improvement in 3-D models. Ship-related particles have large spatiotemporal variations, and their contribution to CCN is driven by secondary particles. Our results support the influence of ship emissions on coastal air aerosols and CCN and highlight the importance of accounting for ship plume subgrid processes.