Measurements on mass size distribution of roadside aerosols were obtained in downtown Jeju City from July 2018 to May 2020 using an 8-stage cascade impactor sampler and the compositions of aerosols were analyzed. The mass size distribution of total aerosols was bimodal with aerosols existing in both the fine and coarse modes. The mass size distributions of Na+, Mg2+, Ca2+, Cl-, NH4 + and SO4 2- were unimodal, whereas that of K+ was bimodal. For NO3 -, the size distribution in winter and spring was bimodal with the peaks in both fine and coarse modes, whereas for summer and autumn the distribution was unimodal with a peak in the coarse mode. NH4 + was found to co-exist with SO4 2- in the fine mode with an average molar ratio of [NH4 +]/[SO4 2-] equal to 2.05. Good correlation was observed between NO3 - and NH4 + in the fine mode particles in spring and winter. Based on the value of the marine enrichment factor for Cl-, Mg2+, K+, Ca2+ and SO4 2-, it may be inferred that a major part of the roadside aerosols in downtown Jeju City was largely contributed by terrigenous sources, although the influence of sea salt was normally present.

To determine the size distributions of water-soluble inorganic ionic species (WSIS) in roadside aerosols, sampling experiments were carried out in the urban roadside area of Jeju City on August 2018 and January 2019 by using the eight-stage cascade impactor sampler. The mass of roadside aerosols were partitioned at 57% in fine fraction, 36-37% in coarse fraction, and 6-7% in giant fraction, regardless of summer and winter. The mass concentrations of WSIS except for Na+ and SO42- in roadside aerosols were higher in winter than in summer. The size distributions of Na+, Mg2+, Ca2+ and Cl- were characterized by bimodal types with coarse particle mode peaking around 3.3-4.7㎛ and 5.8-9.0㎛ . The size distributions of NO3 - and K+ shifted from a single fine mode peaking around 0.7-1.1㎛ in winter to bimodal and/or trimodal types with peaks around coarse mode in summer. SO4 2- and NH4 + showed a single fine mode peaking around 0.7-1.1㎛ . The MMAD of roadside aerosols was lower than that of Na+, Mg2+, Ca2+ and Cl-. Based on the marine enrichment factors and the ratio values of WSIS and the corresponding value for sea water, the composition of roadside aerosols in Jeju City may be practically affected by terrestrial sources rather than marine source.