The chemical compositions of samples of particulate matter up to 2.5 μm in size (PM_2.5)collected from Dingling, Chegongzhuang, Fangshan, and Yufa sites in Beijing, China from August 2012 to July 2013 were analyzed to determine the spatiotemporal characteristics of 15 chemical components, including nitrogen- and sulfur-containing air pollutants and organic carbon (OC) and elemental carbon (EC). The concentrations of OC, SO₄^2-, NO₃^-, and NH₄⁺ were the highest among the 15 chemical components analyzed, and the annual mean concentrations were (22.62±21.86), (19.39±21.06), (18.89±19.82), and (13.20±12.80) μg/m³, respectively. In general, concentrations of the 15 chemical components were highest in winter and lowest in summer, and concentrations were higher in southern areas and lower in northern areas.Concentrationsof NH₄⁺observed in this study were significantly higher than those reported in previous monitoring studies. Concentrations of OC and EC in winter were 3-times and 2.5-times higher, respectively, than the corresponding levels in summer, which was attributed to higher rates of coal consumption in winter. The average ratios of OC/EC in spring, summer, autumn, and winter were 4.9, 7.0, 8.1, and 8.4, respectively, which are indicative of serious pollution levels in Beijing throughout the year. The proportions of secondary organic carbon to OC at the Dingling, Chegongzhuang, Fangshan, and Yufa sites were 57.7%, 60.0%, 45.6%, and 57.6%, respectively, which were calculated based on the OC/EC ratio. The annual ratios of [NO₃^-]/[SO₄^2-] at the Dingling, Chegongzhuang, Fangshan, and Yufa sites were 1.01, 1.25, 1.08, and 1.12, respectively.These data imply that both stationary and mobile sources are important contributors to the poor air quality in Beijing.