Size Distribution and Depolarization Properties of Aerosol Particles over the Northwest Pacific and Arctic Ocean from Shipborne Measurements during an R/V Xuelong Cruise
<p>Atmospheric aerosols over polar regions have attracted considerable attention for their pivotal effects on climate change. In this study, temporospatial variations in single-particle-based depolarization ratios (&#948;: s-polarized component divided by the total backward scattering intensity) were studied over the Northwest Pacific and the Arctic Ocean using an optical particle counter with a depolarization module. The &#948; value of aerosols was 0.06 &#177; 0.01 for the entire observation period, 61 &#177; 10% lower than the observations for coastal Japan (0.12 &#177; 0.02) (Pan et al. Atmos. Chem. Phys. 2016, 16, 9863&#8722;9873) and inland China (0.19 &#177; 0.02) (Tian et al. Atmos. Chem. Phys. 2018, 18, 18203&#8722;18217) in summer. The volume concentration showed two dominant size modes at 0.9 and 2 &#956;m. The super-micrometer particles were mostly related to sea-salt aerosols with a &#948; value of 0.09 over marine polar areas, &#8764;22% larger than in the low-latitude region because of differences in chemical composition and dry air conditions. The &#948; values for fine particles (<1 &#956;m) were 0.05 &#177; 0.1, 50% lower than inland anthropogenic pollutants, mainly because of the complex mixtures of sub-micrometer sea salts. High particle concentrations in the Arctic Ocean could mostly be attributed to the strong marine emission of sea salt associated with deep oceanic cyclones, whereas long-range transport pollutants from the continent were among the primary causes of high particle concentrations in the Northwest Pacific region.</p>