Atmospheric Nitrous Acid in Contrasting Environments in North China

that was correlated to tidal change. At all four sites, HONO contributed significantly to daytime OH production (31-57%), with contributions of ∼50% at two coastal sites. Neglecting HONO chemistry leads to substantial underestimations of radical concentrations and ozone production, particularly at the coastal site where the marine-derived HONO source could contribute to ∼15% of net ozone production. This study provides a comprehensive analysis of HONO sources in contrasting environments and highlights critical knowledge gaps in marine atmospheric HONO chemistry.