Despite low anthropogenic emissions, coastal cities in China frequently experience severe photochemical pollution. To explore the causes of elevated ozone levels in coastal areas and assess the potential role of surrounding marine emissions, we conducted a comprehensive study on atmospheric pollutants at the Haiyan site—a background receptor site in a coastal area of Hangzhou Bay—and seawater pollutants in the East China Shelf Sea. Marine field investigations were conducted onboard the research vessels Xiangyanghong 18 and Dongfanghong 3, covering the potential marine source regions of atmospheric pollutants at the Haiyan site. During the investigation, a ship-based incubation experiment was also performed to investigate the factors influencing marine pollutant emissions and their potential links to atmospheric pollution at the Haiyan site.
The frequent influx of relatively clean maritime air masses generally resulted in lower concentrations of most atmospheric pollutants at the Haiyan site, except for ozone. Notably, photochemical pollution was more severe when the air masses at the Haiyan site originated solely from either the land or the sea. For continental air masses, low wind speeds over the Hangzhou Bay area caused abundant volatile organic compounds (VOCs) emitted from upwind cities to linger longer, promoting the photochemical formation of ozone. Although maritime air masses contained fewer VOCs, the characteristics of emissions from seawater, shipping, and petrochemical parks on surrounding islands resulted in relatively high concentrations and proportions of highly reactive alkenes. Moreover, the higher temperatures and solar radiation in the marine environment significantly accelerated the aging of air masses, which, combined with a weaker NO titration effect, intensified photochemical pollution.
Integrating the marine field survey and land observation, this study identified the significant impact of pollutant emissions from high primary productivity seas on the atmospheric environment of coastal regions, particularly through secondary formation during atmospheric transport. Based on the ship-based incubation experiment, we also observed that terrestrial nutrient inputs substantially increased primary productivity in coastal waters, thereby promoting the production and emission of marine VOCs. The potential link between the eutrophication of coastal seas and air photochemical pollution underscores the critical need for coordinated governance of both air and water pollution to effectively address atmospheric environmental challenges in coastal regions. These findings may apply to other similar coastal environments worldwide.

VOCs O3, coastal city, marine and air pollution, marine emissions, land-sea interactions