Contribution of ship emissions to the concentration of PM2.5: A comprehensive study using AIS data and WRF/Chem model in Bohai Rim Region, China

Compared with on-road vehicles, emission from ships is one of the least-regulated anthropogenic emission sources and non-negligible source of primary aerosols and gas-phase precursors of PM2.5. The Bohai Rim Region in China hosts dozens of large ports, two of which ranked among the top ten ports in the world. To determine the impact of ship emissions on the PM2.5 concentrations over this region, two parts of works have been conducted in this study. First, a detailed ship emission inventory with high spatiotemporal resolution was developed based on Automatic Identification System (AIS) data. Then the WRF/Chem model was applied to modeling the impact of ship emissions by comparing two scenarios: with and without ship emissions. The results indicate that the total estimated ship emissions of SO2, NOX, PM10, PM2.5, CO, HC, and CO2 from Bohai Rim Region in 2014 are 1.9 × 105, 2.9 × 105, 2.6 × 104, 2.4 × 104, 2.5 × 104, 1.2 × 104, and 1.3 × 107 tonnes, respectively. The modeling results indicate that the annual PM2.5 concentrations increased by 5.9% on land areas of Bohai Rim Region (the continent within 115.2°E–124.3°E and 36.1°N–41.6°N) due to ship emissions. The contributions show distinctive seasonal variations of contributions, presenting highest in summer (12.5%) followed by spring (6.9%) and autumn (3.3%), and lowest in winter (0.9%). The contribution reaches up to 10.7% along the shoreline and down to 1.0% 200 km inland. After examining the statistics of the modeling results during heavy and non-heavy haze days in July, it was found that 6 out of 9 cities around the Bohai Rim Region were observed with higher contributions from ship emissions during heavy haze days compared with non-heavy haze days. These results indicate that the impacts of ship emissions on the ambient PM2.5 are non-negligible, especially for heavy haze days for most coastal cities in the Bohai Rim Region.