AbstractConcentrations of nonylphenol isomers (NP), tertiary octylphenol (t-OP) and nonylphenol monoethoxylate isomers (NP1EO) have been simultaneously determined in the sea water and atmosphere of the North Sea. A decreasing concentration profile appeared following the distance increasing from the coast to the central part of the North Sea. Air–sea exchanges of t-OP and NP were estimated using the two-film resistance model based upon relative air–water concentrations and experimentally derived Henry's law constant. The average of air–sea exchange fluxes was −12 ± 6 ng m−2 day−1 for t-OP and −39 ± 19 ng m−2 day−1 for NP, which indicates a net deposition is occurring. These results suggest that the air–sea vapour exchange is an important process that intervenes in the mass balance of alkylphenols in the North Sea.