3.1.2. Principal Factors Composition

The principal factor (*Pi*) is composed of 22 initial factors (*xi*) with a certain proportion coefficient (principal component loading *l*). The absolute value of the loading represents the contribution of the initial factor to a *Pi*, and the positive and negative values represent the influence mode of the initial factor on a *Pi*. Therefore, the principal component of a *Pi* is reflected by the initial factor with relatively high loadings. There were certain differences in the higher loading between different principal factors. Taking *P*<sup>1</sup> as an example, the relationship between it and the initial factor at the overall pollution level is as follows:

*P*<sup>1</sup> = −0.209*x*<sup>1</sup> − 0.18*x*<sup>2</sup> − 0.293*x*<sup>3</sup> + 0.216*x*<sup>4</sup> − 0.248*x*<sup>5</sup> − 0.053*x*<sup>6</sup> − 0.131*x*<sup>7</sup> + 0.116*x*<sup>8</sup> + 0.176*x*<sup>9</sup> + 0.285*x*<sup>10</sup> + 0.012*x*<sup>11</sup> + 0.235*x*<sup>12</sup> + 0.238*x*<sup>13</sup> + 0.315*x*<sup>14</sup> + 0.111*x*<sup>15</sup> + 0.083*x*<sup>16</sup> + 0.125*x*<sup>17</sup> − 0.325*x*<sup>18</sup> + 0.252*x*<sup>19</sup> − 0.281*x*<sup>20</sup> − 0.195*x*<sup>21</sup> + 0.23*x*<sup>22</sup> (4)

where *x*1, *x*2, *x*3,..., *x*<sup>22</sup> are the standardization values of the initial factor.

*Pi* reflects the relationship between each principal factor and its main initial factors. The composition characteristics of each *Pi* can be sorted and summarized according to the corresponding loading. At the overall pollution level, the loading of 22 principal factors was between −1 and 1. The maximum absolute value was 0.685 and the minimum value was 0.0004. The loading of each principal factor at different pollution levels was basically consistent with this, indicating that the composition characteristics of each principal factor were similar.
