A one-year monitoring program from September 2009 to August 2010 for PM10 was conducted at 8 monitoring sites in Tianjin, a coastal city in northern China. 24-hour PM10 samples were collected every 6 days at each site. PM10 samples were analyzed for elements, water soluble inorganic ions and carbonaceous species. This paper focused on the spatial and temporal variation of chemical composition and chemical mass closure of ambient PM10. Six categories were used to reconstruct PM10 mass: crustal materials, trace elements, organic matter, elemental carbon, sea salt, and secondary inorganic aerosol. Crustal materials were the dominant fraction of PM10 with annual average percentages varying from 31.6% to 33.8% of the total PM10 mass. Secondary inorganic aerosol (non-sea salt sulfate, nitrate and ammonium) and organic matter were also major contributors to PM10, with annual mass fractions of 23.3% and 18.8%, respectively. In particular, non-sea salt-sulfate was the most predominant inorganic ion accounting for 47.9% of the category of secondary inorganic aerosol. Elemental carbon was a small category, accounting for 3.3%. Sea salt and trace elements contributed marginally to the PM10 mass. The concentrations and mass fractions of crustal materials were generally highest in spring and lowest in summer while those of organic matter and secondary inorganic aerosol were generally highest in winter. Organic matter (P < 0.05) and elemental carbon (P < 0.001) concentrations showed significant spatial variations, and the concentrations were high at Beichen (BC) due to its proximity to the industrial zones and freeways. The concentrations of Ba, Zn, Pb, Sn, Sb were generally higher at BC and Hongqiao (HQ) than at other sites, suggesting higher influence of traffic emissions.