Impact of halogen chemistry on tropospheric ozone in China

China is a large country with nearly 3 million square kilometers sea area and 32,000 kilometers of coastline, ranking 6th in the world. The interaction between polluted unban and clean marine air parcels greatly affects the air quality in the coastal regions in China, including some significant metropolis such as Shanghai, Guangzhou, Shenzhen, and Hong Kong. Previous studies showed that natural halogens (Cl, Br and I) from ocean play an important role in the atmospheric chemistry, which lead to the chemical reaction of the air in the seaside cities is more complicated than that inland. In this study, the role of marine halogen chemistry has been investigated in China by comparing two chemistry mechanisms (with and without halogen chemistry) in Community Multiscale Air Quality (CMAQ) model. Results indicate that marine halogen can decrease ozone concentration more than 4 ppb in the coastal and marine regions. In severe ozone-polluted areas, the decrease can reach 10 ppb. The simulation without halogen chemistry overestimate the ozone concentration. Therefore, the addition of halogen chemistry can improve the ozone simulation ability to a certain extent. Process analysis of CMAQ can further reveal the change of processes and reactions affected by halogen chemistry.