Table 1.

Types of calibration models used in the literature.

Pollutant	Calibration Model	References	Metrics
CO	LR	Drajic [11], Spinelle [17], Spinelle [18], Topalovic [20], Samad [28], Karagulian [29], Lin [30], Borrego [32]	$R$, $R^2$, RMSE, NRMSE
CO	ANN	Spinelle [17], Spinelle [18], Topalovic [20], Motlagh [23], Alhasa [25], Karagulian [29], Borrego [32]	$R$, $R^2$, RMSE, NRMSE
CO	RF	Karagulian [29], Borrego [32]	$R^2$, RMSE
NO2	LR	Drajic [11], Spinelle [17], Spinelle [18], Cordero [21], Karagulian [29], Borrego [32]	$R^2$, RMSE
NO2	ANN	Spinelle [17], Spinelle [18]. Motlagh [23], Alhasa [25], Samad [28], Karagulian [29], Borrego [32], Espositi [33]	$R^2$, RMSE
NO2	RF	Cordero [21], Karagulian [29], Borrego [32]	$R^2$, RMSE
PM10	LR	Drajic [11], Jayaratne [27], Karagulian [29], Borrego [32]	$R^2$, RMSE
PM10	ANN	Motlagh [23], Karagulian [29], Borrego [32]	$R^2$, RMSE
PM10	RF	Karagulian [29], Borrego [32]	$R^2$, RMSE
PM2.5	LR	Di Antonio [22], Chen [35]	$R^2$, RMSE
PM2.5	ANN	Gao [31], Chang [34], Chen [35]	$R^2$, RMSE
PM2.5	RF	Wang [36]	$R^2$, RMSE