Table 1.

Results of linear regression models (pre-exposure)

	NO2_1 + PD			NO2_1a + PDb + AOD_1c
	AIC	R2	Significant Variables	AIC	R2	Significant Variables
Italy	– 84.9894	0.3863	NO2_1	– 86.8784	0.4651	NO2_1, AOD_1
Germany	– 96.06988	0	Intercept	– 96.06988	0	Intercept
Spain	– 70.5783	0.3223	PD	– 72.2534	0.4106	PD, AOD_1
Italy + Germany	– 123.76349	0.0557	PD	– 123.76349	0.0557	PD
Italy + Spain	– 155.85485	0.2962	NO2_1, PD	– 155.85485	0.2962	NO2_1,PD
Spain + Germany	– 131.67629	0.4075	NO2_1	– 137.45427	0.5135	NO2_1, AOD_1
Italy + Germany + Spain	– 191.25573	0.1208	PD	– 191.25573	0.1208	PD

^aNO2_1: NO₂ from Dec 1, 2019–Feb 29, 2020

^bPD: Population density

^cAOD_1: AOD from Dec 1, 2020 to Feb 29, 2020