Variability of Aerosol Optical Properties in the Asian Continental Outflow Region: Marine background site (Gosan, Korea) vs. high-altitude mountain site (Lulin, Taiwan)

Aerosols play a substantial environmental role due to their effects on air quality and visibility, and their contribution to the Earth's radiation budget through surface cooling or atmospheric warming (Allen et al., Nature Clim. Change, 2016; IPCC, 2013). With relatively short lifetimes and spatial inhomogeneity in emission, aerosols and their radiative effects are important on a local to regional scale, rather than the global scale (Andrews et al., Atmospheric Research, 2011; Collaud Coen et al., Atmos. Chem. Phys. 2013). In this study, we investigated monthly variations of in-situ and columnar aerosol optical properties (AOPs) observed at two regional background sites in the Asian continental outflow; Gosan (33.29°N, 126.17°E, 72 m above mean sea level (amsl); GSN) in Korea and Lulin (23.51°N, 120.92°E, 2,862 m amsl; LLN) in Taiwan, from 2012 to 2014. Differences in monthly variability of AOPs between the two sites were explained with changes in regional-scale meteorological patterns and different air mass sources. Total mean scattering and absorption coefficients for sub-10 µm particles (σ_sp^10µm and σ_ap^10µm) were higher at GSN with mean and standard deviation values of 84.07±79.51 Mm^-1 and 6.10±5.30 Mm^-1, respectively, compared to those of the high altitude mountain site, LLN (31.28±40.13 Mm^-1 and 3.25±4.60 Mm^-1). Peaks in σ_sp^10µm and σ_ap^10µm during May and June at GSN occurred due to accumulation of anthropogenic aerosols resulting from stagnant weather patterns. Substantially high peaks of σ_sp^10µm (68.6 Mm^-1) and σ_ap^10µm (8.14 Mm^-1) during March and April were observed at LLN as a result of transport of aerosols emitted from biomass burning in Northern Indochina and Southern China. Other months, however, showed low σ_sp^10µm (24.20±26.56 Mm^-1) and σ_ap^10μm (2.32±2.70 Mm^-1) due to larger influence of clean free tropospheric air. High light scattering to extinction ratio (SSA) was measured at GSN (0.93±0.03) and LLN (0.90±0.04), with an increase during summer, indicating the high contribution of light scattering aerosols to light extinction. On the other hand, sub-1 μm to sub-10 μm ratios of aerosol scattering and absorption were both smaller at GSN (0.60 and 0.80, respectively) compared to those at LLN (0.84 and 0.95) which is explained by the relatively smaller influence of dust and sea salt aerosols.