Table 2.

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

	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.