Impact of Marine Shipping Emissions on Ozone Pollution During the Warm Seasons in China

As China's land-based anthropogenic emissions are decreasing, the impact of marine shipping emissions (MSEs) on the atmosphere, especially in coastal areas, deserves further attention. This study investigates the impact of MSEs on MDA8 ozone (O3) levels during the warm seasons of 2017 in China, considering different seasons and synoptic patterns. The results indicate that the average impact of MSEs on O3 decreases from offshore to inland, peaking at over 29.0 ppb at sea and 13.8 ppb along the coast of mainland China. Influenced by precursor emissions, meteorology and other factors, MSEs contribute differently to O3 in Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD) and Pearl River Delta (PRD), with contributions of 3.0, 5.2, and 4.9 ppb, respectively, and ranging from 2.7 to 7.3 ppb in 13 coastal port cities. The O3 impacts of MSEs are higher on polluted days than on clean days, especially during onshore winds. In the BTH, MSEs increase O3 by 5.5 ppb on polluted days and 3.0 ppb on clean days with northeast winds from the Bohai Sea. In the YRD, MSEs increase O3 by 9.4 ppb on polluted days and 7.3 ppb on clean days with southeast winds. MSEs significantly increase O3 levels in the PRD by 11.0 ppb on polluted days and 5.0 ppb on clean days with southeast winds. Although the emission inventories, initial and boundary conditions, etc. may introduce uncertainties, our results still provide useful information for O3 pollution management in coastal cities as a reasonable way to track mass contributions. This study looks at how marine shipping emissions (MSEs) affect ozone levels in coastal China during the warm seasons in 2017. The impact of MSEs on ozone levels varies by season and region. They are significant during onshore winds and higher on polluted days than on clean days. They decrease from offshore to inland, peaking at over 29.0 ppb at sea and 13.8 ppb (21.5%) in coastal areas of mainland China. In several port cities, MSEs increase ozone levels by 2.7-7.3 ppb. In the Beijing-Tianjin-Hebei, Yangtze River Delta, and Pearl River Delta, they increase ozone levels by 3.0, 5.2, and 4.9 ppb, respectively. In these three regions, MSEs can increase ozone levels on polluted days (clean days) by 5.5 ppb (3.0 ppb), 9.4 ppb (7.3 ppb), and 11.0 ppb (5.0 ppb) under synoptic patterns with onshore winds. These results show the importance of considering MSEs in managing ozone pollution in coastal cities. Ozone impact of marine shipping emissions (MSEs) decreases from sea to inland, peaking at 29.0 ppb at sea and 13.8 ppb in coastal mainland China In 2017, MSEs increase ozone levels by 2.7-7.3 ppb in coastal port cities and 3.0-5.2 ppb in three major regions MSEs have a higher impact on polluted days and are significant during onshore winds