1194 Figure 3 – Distribution of ERA5 10 m wind speeds during the cold season (operating hours; directions restricted to the central 90% range) 3.3 Estimated Transport Distances and Initial Deposition Areas Based on the parameter settings described in the Methods section, the settling characteristics and theoretical transport distances of airborne particles were calculated. Using Stokes’ law, the transport distances of particles with diameters of 10μm and 30μm were quantitatively estimated. For 10μm particles, the horizontal transport distances were approximately 37 km and 62 km under wind speeds of 4.5 m s⁻¹ and 7.5 m s⁻¹, respectively. In contrast, for 30μm particles, the increased settling velocity substantially reduced the transport distance, resulting in estimated values of approximately 4.1 km and 6.9 km under the same wind conditions. Based on these estimates, the initial deposition areas on the sea surface under the prevailing wind conditions during the cold season are illustrated in Figures 4(a) and 4(b). The distribution for 10μm particles (Figure 4(a)) indicates that the particles were transported over a wide offshore area extending several tens of kilometers from the island. In contrast, the distribution for 30μm particles (Figure 4(b)) shows that deposition was primarily concentrated in the coastal waters near the source area. These comparisons clearly demonstrate that differences in particle size exert a decisive influence on atmospheric transport distances and the spatial distribution of initial deposition patterns. In particular, fine particles corresponding to PM10 pose a potential risk of impacting the marine environment over wide areas, highlighting the importance of considering particle size distribution in marine dispersion analyses. Figure 5 – Marine particle tracking driven by GLORYS12 currents during the cold season: (a) dispersion of PM10-equivalent particles after 39 h, and (b) dispersion of 30μm particles after 4 h. Grey markers show initial positions at entry to the marine domain; red markers show positions at the reported times.
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