. 2015 Mar 3;12(3):e1001792. doi: 10.1371/journal.pmed.1001792

Table 4. Correlation coefficients (Spearman) between air pollutants by season.

	EC (out)	NO₂ (out)	UFP (out)	EC (in)	NO₂ (in)	UPF (in)
EC (out)	0.58^***	0.73^***	0.62^***	0.82^***	0.53^**	0.49^**
NO ₂ (out)	0.63^***	0.49^**	0.51^**	0.61^***	0.71^***	0.34
UPF (out)	0.61^***	0.61^***	0.72^***	0.49^**	0.30	0.57^***
EC (in)	0.86^***	0.69^***	0.63^***	0.73^***	0.66^***	0.61^***
NO ₂ (in)	0.45^**	0.70^***	0.43^*	0.58^***	0.64^***	0.39^*
UFP (in)	0.41^*	0.42^*	0.65^***	0.62^***	0.38^*	0.40^*

Below diagonal, cold season (November–March); above diagonal, warm season (April–October). Correlations between the two seasons in the diagonal.

*p < 0.05

**p < 0.01

***p < 0.001.

out, outdoors (courtyard); in, indoors (classroom).