Characterization of Atmospheric Aerosol over XiAn in the South Margin of the Loess Plateau, China

The mass concentrations of TSP, PM-10, several secondary aerosol species, and up to 20 elements were determined for bulk aerosol samples collected from four ground-based monitoring sites in XiAn, China. The samples were collected during four seasons from September 1996 to August 1997; and in July 1998. Daily concentrations of TSP, SO₂ and NO_x from 1995 to 1997 were also obtained from the same sampling sites. Representative concentrations (annual averages) of TSP, SO₂ and NO_x were 410, 39, 43μgm^-3, respectively. PM-10 accounted for about 60-70% of TSP in summer 1998. The most abundant elements in the samples were Si, Ca, Al, Fe, Cl, P, K and S. A fraction of the Ca, which in typically associated with dust, was from non-crustal sources, especially in coarse particles. In winter, the element with the highest concentration was S, and it was primarily in the form of sulfate. The seasonal mean sulfate concentrations, averaged over all sites, were 100, 340, 59 and 27μgSO^2-₄m^-3 for autumn, winter, spring and summer, respectively. The corresponding loadings of ammonium ion were 49, 140, 40 and 17μgNH₄⁺m^-3 for the same seasons and those for nitrate were 22, 65, 33, 16μgNO₃^-m^-3. Dispersed sources of coal-combustion (most likely residential heating), as opposed to stationary point sources, evidently play an important role in the large increases in TSP and three-fold increases in sulfate, nitrate and ammonium loading during XiAn's space-heating season.