Effect of ship emissions on O3 in the Yangtze River Delta region of China: Analysis of WRF-Chem modeling.

The Yangtze River Delta (YRD) region locates on the eastern coast of China, and it has suffered severe O3 pollutions due to high and mixed emissions of air pollutants. There are 3 different emission sectors for O3 precursors in the region, including anthropogenic VOCS and NOX emissions, ship emissions (mainly NOX), and biogenic emissions from a large forest (biogenic VOCS). This unique emission mixture produces complicated chemical processes in studying the O3 pollutions in the region. This study aims to identify the contribution of the ship emissions to O3 pollutions, as well as the effect of mixing emissions on O3 pollutions in YRD. To identify the individual emission effect, the WRF-Chem model is used in this study. The model generally performs well in simulating meteorological parameters and air pollutants against observations in YRD. Sensitive study suggests that the ship emissions have important effects on the O3 concentrations over ocean and inland, with a maximum increase of 30-50 μg m-3 occurred mainly in the ship track regions. However, the ship emissions have a very complicated effect on the in-land O3 concentrations. In the north of Shanghai, the NOX concentrations are high due to high anthropogenic emissions, and a further increase in NOX emissions from ship results in depressing O3 chemical production. In contrast, in the south of Shanghai, there are high biogenic VOC emissions (mainly isoprene) and low NOx concentrations. As a result, the O3 concentrations are enhanced by 30-50 μg m-3, due to the mixing between ship and forest emissions. This study suggests that ship emissions play important roles in controlling O3 pollutions in YRD. Furthermore, the mixing emissions between ship, anthropogenic, and biogenic emissions in YRD produce a complicated O3 chemical production and need to be carefully considered in controlling strategy of O3 pollution in the region.