*3.2. Characteristics of Chemical Compositions*

The size-fractionated PM are mainly composed of crustal elements, water-soluble ions, and carbonaceous matter. The average mass concentrations of the chemical components at each sampling height in PM10, PM10-2.1, PM2.1, and PM1.1 are shown in Table 3. The characteristics of chemical compositions are discussed in three sections containing elements, water-soluble ions, and carbonaceous matter.

#### 3.2.1. Elements

Elements obtained from Teflon filters were analyzed by an inductively coupled plasma mass spectrometer (ICP-MS, Agilent Technologies, Inc., Model 7500a, Santa Clara, CA, USA). Calibration with reference material (Environmental Calibration Standard, Part 5183- 4688, Agilent Technologies, Santa Clara, CA, USA) demonstrated good linearity and sensitivity for the instrument. The relative standard deviation for each measurement (repeated twice) was within 3%. The method detection limits (MDLs) were determined by adding three standard deviations of the blank readings to the average blank values [26]. The elemental species are classified into three categories: crustal elements such as Al, Ca, Fe, and Mg, heavy metal elements including As, Ba, Cr, Cu, Mn, Ni, Pb, Ti, and Zn, and trace elements including the rest of the elemental species such as Cd, Co, P, Sn, Sr, and V. The most important part of the elements was the crustal elements, which accounted for 85.3%, 79.9%, and 78.8 of all the elements at PM10, PM2.1, and PM1.1, respectively. The crustal elements, heavy metal elements, and trace elements constituted relative fractions varied at different particulate sizes, with higher mass percentages of PM10 and coarse particles than that of fine particulate matter. The mass concentrations of most elements showed a decreasing trend with increasing sampling height, especially in coarse particles, implying that elements were mainly emitted from locally ground fugitive and construction dust. The percentages of chemical compositions in PM10, PM10-2.1, PM2.1, and PM1.1 at different sampling heights are shown in Figure 5. According to CD values of elements in Table 2, the CD values for crustal elements such as Al, Ca, Fe, and Mg were generally less than 0.3 in PM10, PM2.1, and PM1.1 but more than 0.3 in PM10-2.1, indicating larger differences of crustal elements between two heights in coarse particles.

**Figure 5.** The percentages of chemical compositions in (**a**) PM10, (**b**) PM10-2.1, (**c**) PM2.1, and (**d**) PM1.1 at Gulou and Zifeng.
