Acidic gases, NH3 and secondary inorganic ions in PM10 during summertime in Beijing, China and their relation to air mass history

In the summers of 2002–2003, acidic gases, ammonia and water-soluble ions in PM10 were measured in Beijing. The mean concentrations of HCl, HONO, HNO3, SO2 and NH3 are 0.6, 3.6, 1.9, 14.1 and 16.6 μg m−3, respectively, and 2.2, 14.6, 19.3 and 8.9 μg m−3 for Cl-,NO3-,SO42-andNH4+ in PM10. The concentrations of secondary ions in PM10 are found to have strong dependence on the pathway of trajectories. The most frequent southerly air flow is connected with high concentrations of secondary water-soluble ions during summertime. Other trajectories with northwest and north direction lead to lower concentrations of secondary ions. Hebei and Shandong Provinces and the Tianjin Municipality are the main source areas for sulfate as identified by Potential Source Contribution Function. This result emphasizes that the non-Beijing sources play an important role in the sulfate mass concentration in the urban atmosphere of Beijing and validates conclusions based on model calculations for the region.