Source identification, size distribution and indicator screening of airborne trace metals in Kanazawa, Japan

The concentrations of trace metals in aerosols of different sizes in the suburban area of Kanazawa, Japan were determined with inductively coupled plasma mass spectrometry (ICP-MS). The results indicated that, among the anthropogenic elements, the ambient concentration of Zn in the total suspended particles (TSP) was the highest (1386ng/m3) and Cd concentration was the lowest (0.45ng/m3). For the contribution of each particle size fraction to the total metal concentration in aerosols, except for V (33.6%), the “very coarse” aerosol size range (>11μm) contributed a small mass fraction (only 4.05-11.7%). While the “coarse fraction” (11-3.3μm) had the largest mass percentage for most elements. However, the mass percentage of individual metals to the total sum of all investigated metals in each particle size range (from very coarse to very fine) was quite similar, which implied that the coagulation of airborne particles occurred in the study area due to the high humidity over the sampling period. High enrichment factor (EF) values (18.87-1139) were obtained for Zn, Cd, Pb and Cu reflecting the importance of anthropogenic inputs. In contrast, the EF values calculated for V, Ca, Mg, Mn, Sr and Co were low (1.05-15.81) suggesting that they were primarily of natural sources. The concentration ratios of natural sources derived elements (V, Ca, Mg, Mn and Sr) to Fe, and anthropogenic elements (Cd, Pb and Cu) to Zn are quite close in each particle size range, revealing that Fe can be a fine indicator for the prediction of ambient concentrations along with their size distributions of other elements mainly from natural processes, and Zn can be a favorable surrogate for assessment of air pollution resulting from volatile trace elements in this area.