Articles | Volume 16, issue 5
Research article
08 Mar 2016
Research article |  | 08 Mar 2016

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

Daniel Neumann, Volker Matthias, Johannes Bieser, Armin Aulinger, and Markus Quante

Abstract. Coarse sea salt particles are emitted ubiquitously from the ocean surface by wave-breaking and bubble-bursting processes. These particles impact the atmospheric chemistry by affecting the condensation of gas-phase species and, thus, indirectly the nucleation of new fine particles, particularly in regions with significant air pollution. In this study, atmospheric particle concentrations are modeled for the North Sea and Baltic Sea regions in northwestern Europe using the Community Multiscale Air Quality (CMAQ) modeling system and are compared to European Monitoring and Evaluation Programme (EMEP) measurement data. The sea salt emission module is extended by a salinity-dependent scaling of the sea salt emissions because the salinity in large parts of the Baltic Sea is very low, which leads to considerably lower sea salt mass emissions compared to other oceanic regions. The resulting improvement in predicted sea salt concentrations is assessed. The contribution of surf zone emissions is considered separately. Additionally, the impacts of sea salt particles on atmospheric nitrate and ammonium concentrations and on nitrogen deposition are evaluated.

The comparisons with observational data show that sea salt concentrations are commonly overestimated at coastal stations and partly underestimated farther inland. The introduced salinity scaling improves the predicted Baltic Sea sea salt concentrations considerably. The dates of measured peak concentrations are appropriately reproduced by the model. The impact of surf zone emissions is negligible in both seas. Nevertheless, they might be relevant because surf zone emissions were cut at an upper threshold in this study. Deactivating sea salt leads to minor increases in NH3 +  NH4+ and HNO3 +  NO3 and a decrease in NO3 concentrations. However, the overall effect on NH3 +  NH4+ and HNO3 +  NO3 concentrations is smaller than the deviation from the measurements. Nitrogen wet deposition is underestimated by the model at most stations. In coastal regions, the total nitrogen deposition (wet and dry) is considerably affected by sea salt particles. Approximately 3–7 % of atmospheric nitrogen deposition into the North Sea is caused by sea salt particles. The contribution is lower in the Baltic Sea region.

The stations in the EMEP network provide a solid basis for model evaluation and validation. However, for a more detailed analysis of the impact of sea salt particles on atmospheric nitrogen species, size-resolved measurements of Na+, NH4+, and NO3 are needed.

Short summary
Sea salt emissions were updated to be dependent on salinity which improved sodium predictions in the Baltic Sea region. The impact of sea salt on atmospheric nitrate and ammonium concentrations and on nitrogen deposition in the North and Baltic Sea region is assessed. Sea salt has a low effect on nitrate concentrations but does not improve them. 3 to 7 % of the nitrogen deposition into the North Sea is accounted to the presence of sea salt. In the Baltic Sea, the contribution is negligible.
Final-revised paper