Ratios of pollutant levels* contrasting the downwind site and the other two sites (upwind and heavily trafficked) adjusted for change from baseline (2006) to subsequent years
| Contrast | NOx ratio (95% CI) | NO2 ratio (95% CI) | PM10 ratio (95% CI) | PM2.5 ratio 95% CI) | PM1 ratio (95% CI) | |
|---|---|---|---|---|---|---|
| Location | Year | |||||
| Downwind versus (heavily trafficked and upwind)† | 2007/2008 vs 2006‡ | 0.78 (0.61 to 0.99) | 0.77 (0.59 to 1.00) | 1.10 (0.66 to 1.81) | 1.09 (0.55 to 2.16) | 1.06 (0.58 to 1.93) |
| 2007 vs 2006 | 0.59 (0.44 to 0.80) | 0.49 (0.38 to 0.63) | 1.18 (0.61 to 2.28) | 1.04 (0.42 to 2.58) | 0.98 (0.44 to 2.17) | |
| 2008 vs 2006 | 1.02 (0.77 to 1.35) | 1.20 (0.88 to 1.64) | 1.02 (0.56 to 1.85) | 1.14 (0.67 to 1.94) | 1.14 (0.70 to 1.87) | |
| Downwind versus upwind | 2007/2008 vs 2006‡ | 0.84 (0.64 to 1.12) | 0.63 (0.46 to 0.86) | 1.16 (0.65 to 2.07) | 1.10 (0.50 to 2.41) | 1.04 (0.52 to 2.07) |
| 2007 vs 2006 | 0.72 (0.51 to 1.02) | 0.52 (0.39 to 0.71) | 1.16 (0.54 to 2.48) | 1.09 (0.38 to 3.09) | 1.02 (0.41 to 2.55) | |
| 2008 vs 2006 | 0.99 (0.71 to 1.37) | 0.76 (0.53 to 1.09) | 1.16 (0.58 to 2.30) | 1.11 (0.60 to 2.04) | 1.06 (0.60 to 1.87) | |
| Downwind versus heavily trafficked | 2007/2008 vs 2006‡ | 0.72 (0.55 to 0.94) | 0.93 (0.68 to 1.27) | 1.04 (0.58 to 1.86) | 1.09 (0.50 to 2.39) | 1.08 (0.54 to 2.16) |
| 2007 vs 2006 | 0.49 (0.35 to 0.69) | 0.46 (0.34 to 0.61) | 1.20 (0.56 to 2.57) | 1.00 (0.35 to 2.85) | 0.94 (0.38 to 2.36) | |
| 2008 vs 2006 | 1.05 (0.76 to 1.45) | 1.90 (1.33 to 2.72) | 0.89 (0.45 to 1.78) | 1.18 (0.64 to 2.18) | 1.24 (0.70 to 2.19) | |
| Heavily trafficked versus (upwind and downwind)§ | Overall | 4.08 (3.64 to 4.57) | 1.45 (1.28 to 1.65) | 1.27 (1.00 to 1.62) | 1.21 (0.87 to 1.68) | 1.31 (0.99 to 1.75) |
*Ratios are derived from a mixed effects regression model in which location and year, and the interaction between them are fixed effects, and individual intercepts are a random effect. Main contrasts of interest are those included in the table and consist of downwind versus other exposures, as the downwind exposure is the primary exposure of interest in this study.
†Downwind versus (heavily trafficked and upwind) is the comparison of downwind versus heavily trafficked and upwind exposures combined.
‡2007/2008 vs 2006 represents the comparison of both post-tunnel years combined (2007/2008) versus the pre-tunnel year (2006).
§Represents the overall comparison of the heavily trafficked site compared to the two stack sites (downwind and upwind) combined (data from all years included).
NOx, oxides of nitrogen; PM, particulate matter.