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

Abstract

Abstract. Coarse sea salt particles are emitted ubiquitously from the oceans' surfaces by wave breaking and bubble bursting processes. These particles impact atmospheric chemistry by affecting condensation of gas-phase species and nucleation of new fine particles, particularly in regions with high air pollution. In this study, atmospheric particle concentrations are modeled for the North and Baltic Sea regions, Northwestern Europe, using the Community Multiscale Air Quality (CMAQ) modeling system and evaluated against European Monitoring and Evaluation Programme (EMEP) measurement data. As model extension, sea salt emissions are scaled by water salinity because of low salinity in large parts of the Baltic Sea and in certain river estuaries. The resulting improvement in predicted sea salt concentrations is assessed. The contribution of surf zone emissions is separately considered. Additionally, the impact of sea salt particles on atmospheric nitrate, ammonium and sulfate concentrations is evaluated. The comparisons show that sea salt concentrations are commonly overestimated at coastal stations and partly underestimated when going inland. The introduced salinity scaling improves predicted Baltic Sea sea salt concentrations considerably. 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 a minor increase of NH4+ and NO3- and a minor decrease of SO42- concentrations. However, the overall effect is very low and lower than the deviation from measurements. Size resolved measurements of Na+, NH4+, NO3-, and SO42- are needed for a more detailed analysis on the impact of sea salt particles.

A comparison of sea salt emission parameterizations in Northwestern Europe using a chemistry transport model setup

“…The SAL in the Baltic Sea is very low -below 10‰ throughout large regions -which requires the inclusion of an SAL dependence in the sea salt emission calculation. For GO03, the approach described in Neumann et al (2015) was applied:…”

“…In CMAQ (GO03), the surf zone is treated in accordance with Kelly et al (2010) by setting the whitecap coverage W is set to 1 in the surf zone. In this study, calculations of the surf zone size were performed for a 50 m wide surf zone by ArcGIS avoiding double-counting of overlapping surf zone stripes (Neumann et al, 2015). The procedure of setting W to 1 can also be applied for SP13 because MA03 and MO86 depend on the same whitecap coverage parameterization as does GO03 (see Sect.…”

“…The parameterization of sea salt emissions has a long history (e.g., Blanchard and Woodcock, 1980;Fairall et al, 1983;Monahan and Muircheartaigh, 1980) because such parameterizations are necessary in chemistry transport models (CTMs) and climate models because of their impact on atmospheric processes. However, as shown by Gantt et al (2015), Im (2013), and Neumann et al (2015), sea salt concentrations are still not satisfactorily reproduced by CTMs in all situations; thus, improvements to sea salt emission parameterizations are necessary. Extensive reviews of sea salt emissions and emission parameterizations have been published in recent years (Lewis and Schwartz, 2004;de Leeuw et al, 2011;O'Dowd and de Leeuw, 2007;Spada et al, 2013).…”

“…Several were derived from a wind-speed-based parameterization published by Monahan and Muircheartaigh (1980) and Monahan et al (1986). Nevertheless, atmospheric sea salt concentrations are not always predicted with sufficient accuracy (Tsyro et al, 2011;Spada et al, 2013;Neumann et al, 2015), and improving these predictions remains an objective of ongoing research (Ovadnevaite et al, 2014;Gantt et al, 2015;Petelski et al, 2014;Salter et al, 2015;Long et al, 2011).…”