Table 1.
Spatial covariates selected for GAM after removing collinearity.
| Smooth factors | NO2 |
NOx |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Summer |
Winter |
Summer |
Winter |
|||||||||
| V.Pa | Disb | p-value | V.Pa | Disb | p-value | V.Pa | Disb | p-value | V.Pa | Disb | p-value | |
| NDVI | 13.65 | 0.25 | 2.73e-7 | 9.46 | 0.20 | 7.2e-4 | 25.37 | 0.25 | 6.33e-10 | 12.83 | 0.50 | 6.15e-6 |
| Land surface temperature | 1.38 | 1.10 | 0.013 | 6.56 | 0.30 | 0.03 | – | – | – | 12.89 | 0.50 | 0.026 |
| Weighted traffic flow | 4.48 | 13.00 | 5.1e-4 | – | – | – | 2.76 | 13.00 | 0.006 | 8.01 | 15.00 | 5.35e-3 |
| Weighted truck flow | 13.87 | 11.00 | 9.84e-7 | – | – | – | 6.69 | 11.00 | 8.89e-4 | 5.24 | 11.00 | 0.0014 |
| Atmospheric stability | 13.79 | – | 1.27e-7 | – | – | – | 14.29 | – | 4.07e-6 | – | – | |
| Residential land-use proportion | – | – | – | 7.53 | 15.00 | 7.69e-4 | 11.81 | 15.00 | 8.92e-4 | 7.11 | 15.00 | 0.012 |
| Transportation land-use proportion | – | – | – | 7.37 | 15.00 | 5.08e-7 | – | – | – | 15.96 | 15.00 | 3.9e-10 |
| Farm and open land-use proportion | – | – | – | 10.52 | 2.50 | 7.23e-4 | – | – | – | 1.92 | 3.00 | 0.0036 |
| Local road length (A4) | 5.97 | 15.00 | 1.87e-4 | – | – | – | – | – | – | – | – | – |
| Minimal distance to major freeways (A1) | – | – | – | 16.54 | – | 6.16e-8 | – | – | – | – | – | – |
| Minimal distance to local streets (A4) | 14.85 | – | 7.24e-7 | – | – | – | 5.12 | – | 1.21e-4 | – | – | – |
a
V.P: the percent of variance explained by the variable (%).
b
Dis: optimal buffering distance (unit: km).