The lag lengths of the variables and whether or not to input
to ANN models were determined by analyzing PCA results.
The correlation coefficient values (r) were used in PCA runs.
The correlation results were appropriate to use the PCA, as r
values were generally ≥0.3. However, RH did not exhibit a
significant correlation with the others; thus, it was placed
neither in the PCA variables nor in ANN models as input. AT
showed a negative correlation with PM10 (r = −0.698) and a
moderately strong correlation with the other explanatory variables,
which indicates the seasonal pollution effect due to
residential heating controlled by meteorological factors.
PCA was applied to actual PM10 data on day t (PM10t)
against the variables lagged by seven times. Since the variable
RH was removed, four PCA runs were performed between
PM10t and the lagged terms of its own and the retaining
variables in the lagged data set. Table 3 shows the extracted
principal components (PCs), with the percentage of explained
variance by this factor in parenthesis, and loading scores on