*2.6. Statistical Analysis*

In this study, we used Statistical Package for Social Sciences (SPSS) for Windows (IBM SPSS Statistics, Version 25) to find the Pearson's correlation coefficient for criteria pollutants on an annual and seasonal basis [48], and used RStudio for graphical representation [49]. The high (low) value of the Pearson's correlation represents the same (different) variations in one criteria pollutant with respect to another pollutant. The effect of a certain variable was considered statistically significant for P (0.01, and 0.05) (two-tailed). Annual mean values, mean absolute deviation (MAD), mean square error (MSE), root mean square error (RMSE), mean absolute percentage error (MAPE), and mean percentage error (MPE) of six criteria pollutants between 2015 and 2018 were calculated by Microsoft Excel 2016.
