3.2.2. IEs Levels

The concentrations of IEs in PM2.5 in the two seasons are shown in Figure 4. The concentrations of IEs in PM2.5 were 4.82 μg/m<sup>3</sup> and 4.10 μg/m<sup>3</sup> in spring and autumn, respectively. Fifteen main elements, Ti, Si, Ca, Fe, Al, K, Mg, Na, Sb, Zn, P, Pb, Mn, As and Cu, account for 99.38% and 99.24% of the total inorganic elements in spring and autumn, respectively. These fifteen elements play a key role in the estimation of emission sources and are associated with human activity (such as industrial processes, residential activities, and traffic patterns).

**Figure 4.** Mean concentrations of inorganic elements in PM2.5 sampled at Wenshan.

In the PM2.5 samples, the relatively high concentrations of elements are in the order of Ti>Si>Ca>Al>Fe>K>Mg>Na>Sb>Zn>P>Pb>Mn>As>Cu (spring) and Ti>Si>Ca>Fe>Al>K> Mn>Mg>Na>Zn>Sb>Pb>P>As>Cu (autumn). The fifteen main IE concentrations accounted for 14.88% of the total PM2.5 in spring and 14.89% in autumn. The concentrations of the identified elements of soil dust (Ti, Si, Al, Ca, Mg) were 5.24 μg/m<sup>3</sup> in spring and 4.29 μg/m3 in autumn, which showed that surface dust was the main source of PM2.5. The concentrations of the industrial discharge elements (As, Zn, and Mn) were 0.10 μg/m<sup>3</sup> in spring and 0.38 μg/m3 in autumn. The concentration of Pb was 0.03 μg/m3 in spring and 0.06 μg/m<sup>3</sup> in autumn, and it may be due to motor vehicle exhaust emissions. The concentrations of K accounted for 1.35% of PM2.5 in spring and 0.99% in autumn, which may be due to biomass burning [59–61].
