The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

1594 / 2024-10-13 16:05:37

Chemical interaction of anthropogenic and oceanic emission and its impact on air quality in coastal cities

Halogens,oxidation,ozone,PM2.5,Hg

Chlorine (Cl) and bromine (Br) atoms are highly reactive and can strongly influence atmospheric abundances of climate and air quality-relevant trace gases such as methane and ozone (O₃). We observed high concentrations of Cl₂ and Br₂ during daytime in a coastal area in Hong Kong, indicating the presence of a large daytime source as the photolytic lifetime of Cl₂ and Br₂ is only ~7 and ~4 minutes at noon, respectively. This source was positively correlated with the product of solar actinic flux, nitrate and aerosol surface areas, suggesting a photochemical source involving nitrate and occurring at air-particle interface. Illuminating acid doped nitrate-NaCl solution with a xenon lamp in laboratory revealed that photolysis of particulate nitrate under acidic conditions could activate chloride and bromide. Chemical box model constrained by the observation data shows that the Cl₂ and Br₂, through photodissociation to produce Cl and Br, atoms, significantly increases the atmospheric oxidation rate of volatile organic compounds (VOCs), conventional RO_x radical, O₃ production, and Hg oxidation. Chemical transport model also demonstrates considerable impact on ozone and PM_2.5 in the coastal areas. Our study suggests the need for considering this new pollution-induced activation of sea salt halogens and its impact on atmospheric chemistry and air quality in coastal areas.