Surface Ozone in the Marine Environment—Horizontal Ozone Concentration Gradients in Coastal Areas
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Spring/summer surface ozone concentrations, [O3], in coastal environments were investigated: (1) by comparison of coastal and inland monitoring stations with data from a small island >5 km off the coast of southwest Sweden, (2) as a gradient from the coast towards inland in southernmost Sweden. Further, results from the chemical transport model MATCH were used to assess the marine influence on [O3]. It was hypothesised that [O3] is higher on the small island compared to the coast, especially during night and in offshore wind. Another hypothesis was that [O3] declines from the coast towards inland. Our hypotheses were based on observations that the deposition velocity of O3 to sea surfaces is lower than to terrestrial surfaces, and that vertical air mixing is stronger in the marine environment, especially during night. The island experienced 10 % higher [O3] compared to the coast. This difference was larger with offshore (15 %) than onshore wind (9 %). The concentration difference between island and coast was larger during night, but prevailed during day and could not be explained by differences in [NO2] between the sites. The difference in [O3] between the island and the inland site was 20 %. Higher [O3] over the sea, especially during night, was reproduced by MATCH. In the gradient study, [O3] declined from the coast towards inland. Both [O3] and [NO2] were elevated at the coast, indicating that the gradient in [O3] from the coast was not caused by NO titration. The conclusions were that surface [O3] in marine environments is higher than in coastal, and higher in coastal than inland areas, especially during night.
KeywordsOzone Wind direction Coast Marine boundary layer Terrestrial boundary layer Nitrogen dioxide
Thanks are due to the County Administration Boards of Västra Götaland, Halland and Skåne, Kalmar, Blekinge, Kronoberg and Jönköping as well as the Helge Ax:son Johnson Foundation and the Adlerbert Research Foundation for funding the measurements. Thanks also to Bo Lind, Annette Åberg, Rickard Hansson, Rolf Mårtensson, Gunilla Mårtensson, Mats Ingvarsson, Ingvar Andersson, Dick von Blixen Finecke, Ingela Dejenfeldt, Hans Andersson, Kristian Lillö and Anna Tengberg in Skåne, to Uno Unger at the Nidingen Ornithological Station and Calle Sjöberg for assistance with the measurements. The publication of this paper was funded by the CLEO research programme of the Swedish Environmental Protection Agency.
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