Table 3.
Relative importance (%) of the predictors in Stage-3 for the first, middle, and last years.
| Stage-3 Predictors | 2008 | 2013 | 2018 |
|---|---|---|---|
| EMEP4UK PM2.5 | 32.41 | 32.83 | 36.74 |
| Spatially-lagged hotspot-PM2.5 regional | 2.55 | 2.49 | 6.77 |
| Wind direction | 6.35 | 7.33 | 5.34 |
| Spatially-lagged background-PM2.5 regional | 1.14 | 6.06 | 4.93 |
| Day of the year | 3.22 | 4.33 | 3.73 |
| Spatially-lagged hotspot-PM2.5 local | 3.97 | 1.65 | 3.66 |
| Precipitation | 6.63 | 2.42 | 3.25 |
| BLH 0h | 2.28 | 2.91 | 2.79 |
| Spatially-lagged background-PM2.5 local | 0.94 | 3.07 | 2.75 |
| Month | 1.76 | 2.72 | 2.68 |
| 2m Air temperature | 2.60 | 2.93 | 2.65 |
| Wind speed | 3.08 | 3.75 | 2.53 |
| Sea-level pressure | 3.09 | 2.60 | 2.49 |
| Relative humidity | 1.77 | 1.56 | 1.81 |
| Nearest non-traffic monitor distance | 3.10 | 2.30 | 1.78 |
Note: The top 15 predictors in the RF importance ranking order is determined by the year 2018. The importance is measured by the amount of error reduced due to the splits of a given predictor over all trees used in the RF ensemble.