Articles | Volume 16, issue 18
Atmos. Chem. Phys., 16, 12081–12097, 2016
Atmos. Chem. Phys., 16, 12081–12097, 2016

Research article 27 Sep 2016

Research article | 27 Sep 2016

Sea salt emission, transport and influence on size-segregated nitrate simulation: a case study in northwestern Europe by WRF-Chem

Ying Chen1,2, Yafang Cheng2, Nan Ma1,2, Ralf Wolke1, Stephan Nordmann3, Stephanie Schüttauf1, Liang Ran4, Birgit Wehner1, Wolfram Birmili1,3, Hugo A. C. Denier van der Gon5, Qing Mu2, Stefan Barthel1, Gerald Spindler1, Bastian Stieger1, Konrad Müller1, Guang-Jie Zheng6, Ulrich Pöschl2, Hang Su2, and Alfred Wiedensohler1 Ying Chen et al.
  • 1Leibniz Institute for Tropospheric Research, 04318 Leipzig, Germany
  • 2Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 3German Environment Agency, 06844 Dessau-Roßlau, Germany
  • 4Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
  • 5Dept. of Climate, Air and Sustainability, TNO, Princetonlaan 6, 3584 CB Utrecht, the Netherlands
  • 6State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China

Abstract. Sea salt aerosol (SSA) is one of the major components of primary aerosols and has significant impact on the formation of secondary inorganic particles mass on a global scale. In this study, the fully online coupled WRF-Chem model was utilized to evaluate the SSA emission scheme and its influence on the nitrate simulation in a case study in Europe during 10–20 September 2013. Meteorological conditions near the surface, wind pattern and thermal stratification structure were well reproduced by the model. Nonetheless, the coarse-mode (PM1 − 10) particle mass concentration was substantially overestimated due to the overestimation of SSA and nitrate. Compared to filter measurements at four EMEP stations (coastal stations: Bilthoven, Kollumerwaard and Vredepeel; inland station: Melpitz), the model overestimated SSA concentrations by a factor of 8–20. We found that this overestimation was mainly caused by overestimated SSA emissions over the North Sea during 16–20 September. Over the coastal regions, SSA was injected into the continental free troposphere through an “aloft bridge” (about 500 to 1000 m above the ground), a result of the different thermodynamic properties and planetary boundary layer (PBL) structure between continental and marine regions. The injected SSA was further transported inland and mixed downward to the surface through downdraft and PBL turbulence. This process extended the influence of SSA to a larger downwind region, leading, for example, to an overestimation of SSA at Melpitz, Germany, by a factor of  ∼  20. As a result, the nitrate partitioning fraction (ratio between particulate nitrate and the summation of particulate nitrate and gas-phase nitric acid) increased by about 20 % for the coarse-mode nitrate due to the overestimation of SSA at Melpitz. However, no significant difference in the partitioning fraction for the fine-mode nitrate was found. About 140 % overestimation of the coarse-mode nitrate resulted from the influence of SSA at Melpitz. In contrast, the overestimation of SSA inhibited the nitrate particle formation in the fine mode by about 20 % because of the increased consumption of precursor by coarse-mode nitrate formation.

Short summary
Sea salt aerosol (SSA) is important for primary and secondary aerosols on a global scale. During 10–20 September 2013, the SSA mass concentration was overestimated by a factor of 8–20 over central Europe by WRF-Chem model, stem from the uncertainty of its emission scheme. This could facilitate the coarse-mode nitrate formation (~ 140 % but inhibit the fine-mode nitrate formation (~−20 %). A special long-range transport mechanism could broaden this influence of SSA to a larger downwind region.
Final-revised paper