The characteristics of water-soluble ions in airborne particulate matter in Beijing were investigated using ion chromatography. The results showed that the total concentrations of ions were 83.7 ± 48.9 μg/m(3) in spring, 54.0 ± 17.0 μg/m(3) in summer, 54.1 ± 42.9 μg/m(3) in autumn, and 88.8 ± 47.7 μg/m(3) in winter, respectively. Furthermore, out of all the ions, NO3(-), SO4(2-) and NH4(+) accounted for 81.2% in spring, 78.5% in summer, 74.6% in autumn, and 76.3% in winter. Mg(2+) and Ca(2+) were mainly associated with coarse particles, with a peak that ranged from 5.8 to 9.0 μm. Na(+), NH4(+) and Cl(-) had a multi-mode distribution with peaks that ranged from 0.43 to 1.1 μm and 4.7 to 9.0 μm. K(+), NO3(-), and SO4(2-) were mainly associated with fine particles, with a peak that ranged from 0.65 to 2.1 μm. The concentrations of Na(+), K(+), Mg(2+), Ca(2+), NH4(+), Cl(-), NO3(-) and SO4(2-) were 2.69, 2.32, 1.01, 4.84, 16.9, 11.8, 42.0, and 44.1 μg/m(3) in particulate matter (PM) on foggy days, respectively, which were 1.4 to 7.3 times higher than those on clear days. The concentrations of these ions were 2.40, 1.66, 0.92, 4.95, 17.5, 7.00, 32.6, and 34.7 μg/m(3) in PM on hazy days, respectively, which were 1.2-5.7 times higher than those on clear days.