This project evaluates the effectiveness of Sheffield's Clean Air Zone (CAZ), implemented on 27 February 2023, in reducing nitrogen dioxide (NO₂) concentrations. Using daily air quality data from the Copernicus Atmosphere Monitoring Service (CAMS), we apply interrupted time series regression and distributional analysis to quantify the intervention's impact on urban air quality.
- RQ1 (CAZ Effectiveness): Did Sheffield's NO₂ concentrations significantly decrease after the CAZ implementation?
- RQ2 (Seasonal Patterns): Was the improvement consistent across all seasons, or concentrated in specific months?
- 10.7% reduction in mean NO₂ concentration (13.5 → 12.1 μg/m³)
- Statistically significant improvement (p < 0.001, Cohen's d = 0.21)
- All 12 months show decreased pollution post-CAZ
- WHO-compliant days increased from 45% to 62%
- Unhealthy days (>20 μg/m³) dropped from 18% to 8%
| Figure | Purpose | Key Finding |
|---|---|---|
| Fig 1: Executive Dashboard | Time series overview | 10.7% mean reduction with statistical significance |
| Fig 2: ITS Regression | Causal inference | Immediate drop + sustained decline post-intervention |
| Fig 3: Slope Graph | Monthly breakdown | All months improved; winter saw largest gains |
| Fig 4: Sankey Diagram | Distributional flow | Shift from unhealthy to WHO-compliant days |