| Summary: | In this study, the ionic and carbonaceous compounds in PM<sub>2.5</sub> were analysed in the small residential city of Chuncheon, Korea. To identify the local sources that substantially influence PM<sub>2.5</sub> concentrations, the samples were divided into two groups: samples with PM<sub>2.5</sub> concentrations higher than those in the upwind metropolitan area (Seoul) and samples with lower PM<sub>2.5</sub> concentrations. During the sampling period (December 2016–August 2018), the average PM<sub>2.5</sub> was 23.2 μg m<sup>−3</sup>, which exceeds the annual national ambient air quality standard (15 μg m<sup>−3</sup>). When the PM<sub>2.5</sub> concentrations were higher in Chuncheon than in Seoul, the organic carbon (OC) and elemental carbon (EC) concentrations increased the most among all the PM<sub>2.5</sub> components measured in this study. This is attributable to secondary formation and biomass burning, because secondary OC was enhanced and water soluble OC was strongly correlated with K<sup>+</sup>, EC, and OC. A principal component analysis identified four factors contributing to PM<sub>2.5</sub>: fossil-fuel combustion, secondary inorganic and organic reactions in biomass burning plumes, crustal dust, and secondary NH<sub>4</sub><sup>+</sup> formation.
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