Table 3.

Model selection-Step 3-NO${}_2$: Best subset of covariates using backward-forward stepwise algorithms for NO${}_2$.

	Marche		Verziere		Senato		Liguria		Citta Studi
	AIC	BIC	AIC	BIC	AIC	BIC	AIC	BIC	AIC	BIC
Holidays	✓	✓	✓	✓	✓	✓	✓	✓	✓	✓
Week-End	✓	✓	✓	✓	✓	✓	✓	✓	✓	✓
Saturday:Holidays	✓		✓		✓		✓	✓	✓
Sunday:Holidays	✓	✓	✓	✓	✓	✓	✓		✓	✓
Wind speed Q${}_{\mathrm{NE}}$
Wind speed Q${}_{\mathrm{SE}}$
Wind speed Q${}_{\mathrm{SW}}$	✓	✓	✓	✓	✓	✓	✓	✓	✓	✓
Wind speed Q${}_{\mathrm{NW}}$	✓								✓
Temperature
Rainfall			✓		✓
Global radiation	✓		✓		✓				✓
Humidity	✓								✓

Note: symbol ✓ indicates that the regressor is selected within the best subset of covariates.