Nitric oxide (NO) seems to be widespread, with different functions in the marine ecosystem, but we know little about it. Concentrations of NO were in a range from below the limit of detection to 616 pmol L⁻¹ at the surface and 482 pmol L⁻¹ at the bottom of the Bohai and Yellow seas. The study region was a source of atmospheric NO. Net NO sea-to-air fluxes were much lower than NO photoproduction rates, implying that the NO produced in the mixed layer was rapidly consumed before entering the air.