To investigate the chemical characteristics and sources of size-segregated particles in the background region, PM1.0, PM2.5 and PM10 samples were collected in Tuoji Island (TI) during the winter of 2014. Water-soluble inorganic ions (WSIIs) including Na+, NH4+, K+, Mg2 +, Ca2 +, Cl−, NO3− and SO42 −, organic carbon (OC) and elemental carbon (EC) and water-soluble organic carbon (WSOC) were analysed. The average mass concentrations of PM1.0, PM2.5 and PM10 were 44.5 μg/m3, 62.0 μg/m3 and 94.4 μg/m3, respectively, and particles were importantly enriched in PM1.0. Secondary WSIIs (NH4+, NO3− and SO42 −) were the most abundant species, and their contribution was highest in PM1.0. The average values of NOR and SOR were more than 0.1 in PM1.0, suggesting that secondary formation of SO42 − and NO3− from the gas precursors SO2 and NO2 occurred in PM1.0. Secondary organic carbon accounted for 62.3% in PM1.0, 61.9% in PM1.0–2.5 and 48.9% in PM2.5–10 of OC, formed mainly in the fine mode. The particles concentrations were mainly affected by air mass from the North China Plain, especially the air mass from the southwest of Shandong province, which had low speed and altitude.