Conclusion
The main goal of this study was to improve ANN model
predictions of PM10 levels 1 day ahead by applying PCA
method in the selection of the most significant lagged terms
of the variables as inputs, developing seasonal ANN models
for winter and summer periods, and comparing singular ANN
models as benchmark. The most significant lagged inputs
were three consecutive lags of PM10 and AT according to
PCA runs. In training of ANN models, cascading-training
procedure provided by FANN library was employed, which
produced reasonably successful models. It may thus be an
alternative way to determine the right number of hidden units
in the middle layer of ANNs. For seasonal ANN models, the
overall model agreement in training between modeled and
observed values varied in the range of 0.78–0.83 and R2
values ranged in 0.681–0.727. The best testing R2 values of
seasonal models for winter and summer period models ranged
in 0.709–0.711, with lower testing RMSE values comparing
with the nonseasonal models. Also, seasonal models did not
show a tendency towards overpredicting or underpredicting
the daily average PM10 levels 1 day ahead with better estimates.
This approach appeared to be promising in capturing
nonlinear features in data and could have significant applicability
in the case of the data sets with a large number of
considered inputs.