Sensitivity of modeled atmospheric nitrogen species and nitrogen deposition to variations in sea salt emissions in the North Sea and Baltic Sea regions

摘要

Coarse sea salt particles are emitted ubiquitously from the ocean surface bywave-breaking and bubble-bursting processes. These particles impact theatmospheric chemistry by affecting the condensation of gas-phase species and,thus, indirectly the nucleation of new fine particles, particularly inregions with significant air pollution. In this study, atmospheric particleconcentrations are modeled for the North Sea and Baltic Sea regions innorthwestern Europe using the Community Multiscale Air Quality (CMAQ)modeling system and are compared to European Monitoring and EvaluationProgramme (EMEP) measurement data. The sea salt emission module is extendedby a salinity-dependent scaling of the sea salt emissions because the salinityin large parts of the Baltic Sea is very low, which leads to considerablylower sea salt mass emissions compared to other oceanic regions. The resultingimprovement in predicted sea salt concentrations is assessed. The contribution ofsurf zone emissions is considered separately. Additionally, the impacts ofsea salt particles on atmospheric nitrate and ammonium concentrations and on nitrogendeposition are evaluated.The comparisons with observational data show that sea salt concentrations arecommonly overestimated at coastal stations and partly underestimated fartherinland. The introduced salinity scaling improves the predicted Baltic Sea seasalt concentrations considerably. The dates of measured peak concentrationsare appropriatelyreproduced by the model. The impact of surf zone emissions is negligible in bothseas. Nevertheless, they might be relevant because surf zone emissions were cut atan upper threshold in this study. Deactivating sea salt leads to minor increases inNH +  NH and HNO +  NO and a decrease inNO concentrations. However, the overall effect onNH +  NH and HNO +  NO concentrations is smaller than the deviationfrom the measurements. Nitrogen wet deposition is underestimated by the modelat most stations. In coastal regions, the total nitrogen deposition (wet anddry) is considerably affected by sea salt particles. Approximately3–7 % of atmospheric nitrogen deposition into theNorth Sea is caused by sea salt particles. The contribution is lower in theBaltic Sea region.The stations in the EMEP network provide a solid basis for model evaluationand validation. However, for a more detailed analysis of the impact of seasalt particles on atmospheric nitrogen species, size-resolved measurements ofNa, NH, and NO are needed.