We investigated variability of in-situ and columnar aerosol optical properties (AOPs) at two regional background sites in the Asian continental outflow from 2012 to 2014. The monthly variability of AOPs at each site was explained using regional-scale atmospheric circulation patterns and the resulting changes in air mass sources. The median aerosol scattering and absorption coefficient values for sub-10 μm particles (σsp10 μm and σap10 μm) at the polluted marine site, Gosan (GSN; σsp10 μm: 59.94 Mm-1, σap10 μm: 4.73 Mm-1), were larger than those of the high-altitude mountain site, Lulin (LLN; σsp10 μm: 17.07 Mm-1, σap10 μm: 1.72 Mm-1). Elevated σsp10 μm and σap10 μm at GSN in May and June can be explained by the accumulation of locally emitted aerosols together with long-range transported aerosols under stagnant synoptic patterns, enhanced particle formation and subsequent growth. The significant peaks of σsp10 μm and σap10 μm, with median values of 50.76 Mm-1 and 5.92 Mm-1, at LLN during March and April can be attributed to biomass burning aerosols transported from Northern Indochina and Southern China. The LLN site was mostly influenced by clean free tropospheric air and maritime air masses during the other months, showing medians of 14.65±19.81 Mm-1 and 1.46±1.86 Mm-1 in σsp10 μm and σap10 μm, respectively. Smaller median values of the sub-micron to sub-10 μm ratio of aerosol scattering (0.60) and absorption (0.81) at GSN, compared to LLN (0.81 and 0.91, respectively), are indicative of the larger proportion of coarse aerosols such as sea salt and dust at GSN. Single scattering albedo for sub-10 μm particles showed similar median values at both sites (GSN: 0.93±0.02, LLN: 0.91±0.03).