Table 3.
Summary statistics for covariates evaluated in mixed effects regression models of outdoor residential UFP concentration.
| Covariate | Mean ± SD | Median | Range |
|---|---|---|---|
| Residential covariates (N=16)* | |||
|
| |||
| Side of highway | 13 homes west of highway |
3 homes east of highway |
|
| Residential distance from highway (m) |
367 ± 466 | 152 | 33 – 1,483 |
|
| |||
| Hourly covariates (up to N=4,029) | |||
|
| |||
| Traffic Volume (vehicles/hour) | 6,428 ± 3,169 | 7,832 | 205 – 11,477 |
| Traffic speed (mph) | 56.6 ± 7.8 | 59.9 | 17.6 – 65.4 |
| Temperature (°C) | 21.4 ± 6.1 | 21.9 | 1.9 – 36.4 |
| Wind speed (m/s) | 2.2 ± 1.3 | 2.1 | 0 – 8.4 |
| Wind direction† | |||
| East | 0.21 ± 0.36 | - | - |
| West | 0.36 ± 0.43 | - | - |
| Northwest | 0.30 ± 0.39 | - | - |
| Southeast | 0.12 ± 0.30 | - | - |
| Precipitation (inches/hour) | 0.01 ± 0.04 | 0 | 0 – 0.72 |
Abbreviations: UFP, ultrafine particles; SD, standard deviation; mph, miles per hour.
*
Two homes were missing concurrent data with the near highway fixed monitors and thus were excluded from this analysis.
†
The proportion of 5-minute intervals during which the wind was from the given direction.