Technical Appendix
Monitoring Methodology and Technical Data for Putney Air Quality Study
1. Monitoring Locations and Infrastructure
The Putney Society has maintained a comprehensive monitoring network since 2011. As of 2025, the monitoring infrastructure consists of:
Council Monitoring Stations
Wandsworth Council maintains two official monitoring stations on Putney High Street, providing continuous real-time data for NO₂ and particulate matter.
BreatheLondon Network
Three additional monitors installed by the BreatheLondon initiative provide supplementary coverage of the area.
Putney Society Diffusion Tube Network
Since July 2022, the Putney Society has worked with Wandsworth Council’s Environmental Health Team to maintain diffusion tubes at the following locations:
- PY1: Next to Star & Garter on Lower Richmond Road
- PY2: Outside the Odeon cinema
- PY3: Putney Bridge Road at Burstock Road
- PY4: Opposite the Odeon
- PY5: By the Bus garage on Chelverton Road
- PY6: Upper Richmond Road opposite Putney Hotel
- PY7: Putney Cross near KFH
- PY8: Upper Richmond Road near Putney Common
These tubes are replaced monthly and analysed by accredited laboratories to ensure data quality and consistency.
2. Measurement Methodology
Nitrogen Dioxide (NO₂) Measurement
NO₂ is measured using two primary methods:
- Continuous analysers: The council monitoring stations use chemiluminescence analysers providing hourly readings. These meet EU reference method standards (EN 14211:2012).
- Diffusion tubes: Palmes-type passive diffusion tubes exposed for four-week periods. These provide time-weighted average concentrations and are analysed using UV spectrophotometry. Tubes are bias-adjusted using co-location studies with continuous analysers.
Particulate Matter (PM) Measurement
PM10 and PM2.5 are measured using:
- TEOM-FDMS (Tapered Element Oscillating Microbalance with Filter Dynamics Measurement System)
- BAM (Beta Attenuation Monitor) instruments
Both methods are EU reference method equivalent and provide hourly data.
3. Data Quality Assurance
Quality assurance procedures include:
- Regular calibration of continuous monitors (every 3 months)
- Annual independent audits by UKAS-accredited organisations
- Duplicate and triplicate diffusion tube deployment at 20% of sites
- Bias adjustment factors calculated annually from co-location studies
- Data capture requirements: minimum 75% for annual statistics
- Participation in national QA/QC schemes (WASP, AIR-PT)
4. Historical Data Summary
Annual mean NO₂ concentrations at Putney High Street kerbside monitor:
| Year | NO₂ (μg/m³) | Status vs Legal Limit (40 μg/m³) |
|---|---|---|
| 2011 | 147 | 3.7x over limit |
| 2012 | 155 | 3.9x over limit |
| 2013 | 148 | 3.7x over limit |
| 2014 | 142 | 3.6x over limit |
| 2015 | 137 | 3.4x over limit |
| 2016 | 125 | 3.1x over limit |
| 2017 | 76 | 1.9x over limit |
| 2018 | 72 | 1.8x over limit |
| 2019 | 68 | 1.7x over limit |
| 2020 | 58 | 1.5x over limit (COVID impact) |
| 2021 | 62 | 1.6x over limit |
| 2022 | Limited data | – |
| 2023 | 35 | Below limit |
| 2024 | 34 | Below limit |
| 2025 | 33 | Below limit |
5. Hourly NO₂ Exceedances
Number of hours exceeding 200 μg/m³ (legal limit: 18 hours per year):
- 2012: 2,740 hours
- 2013: 1,858 hours
- 2014: 1,624 hours
- 2015: 1,486 hours
- 2016: 1,272 hours
- 2017: 76 hours
- 2018: 45 hours
- 2019: 38 hours
- 2020: 12 hours
- 2021: 28 hours
- 2023: 8 hours
- 2025: 3 hours
6. Bus Fleet Technical Evolution
The transformation of the bus fleet serving Putney High Street:
2011-2012: Baseline Fleet
- 177 diesel buses
- 76% Euro III standard or below
- Contributing 68% of NOx emissions
2012-2013: First Interventions
- 46 worst-polluting buses replaced
- 10 new hybrid buses introduced
- 85 buses retrofitted with SCR technology
2013-2016: Retrofit Programme
- 94 double-decker buses fitted with SCR
- Up to 88% NOx reduction per bus (in laboratory conditions)
- Real-world reductions approximately 40-60%
2017-2020: Hybrid Rollout
- New generation hybrid buses on major routes
- Euro VI standard compliance
- 40% reduction in street-level NO₂
2021-2025: Electric Transition
Routes converted to electric:
- 2023: Route 93
- 2023-2024: Routes 39, 265, 337
- Remaining diesel routes: 14, 85, 430 (scheduled for conversion)
7. Legal Framework and Standards
Air quality limits derive from EU Directive 2008/50/EC, transposed into UK law:
Nitrogen Dioxide Limits
- Annual mean: 40 μg/m³
- Hourly mean: 200 μg/m³ (not to be exceeded more than 18 times per year)
Particulate Matter Limits
PM10:
- Annual mean: 40 μg/m³
- Daily mean: 50 μg/m³ (not to be exceeded more than 35 times per year)
PM2.5:
- Annual mean: 25 μg/m³ (20 μg/m³ WHO guideline)
8. Source Apportionment Data (TRL Study 2011)
NOx emissions by vehicle type on Putney High Street:
| Vehicle Type | % of Traffic Flow | % of NOx Emissions |
|---|---|---|
| Buses | 10% | 68% |
| Cars | 66% | 14% |
| LGVs | 15% | 9% |
| HGVs | 5% | 7% |
| Taxis | 3% | 2% |
| Motorcycles | 1% | <1% |
9. Key Technical References
Wandsworth Council Annual Status Reports (2011-2025)
TRL Report PPR595 (2011): Emissions source apportionment study for Putney High Street
King’s College London ERG (2016): Putney High Street air quality analysis
Defra Technical Guidance LAQM.TG(22): Local Air Quality Management guidance
WHO Global Air Quality Guidelines (2021)
Transport for London Bus Fleet Audit Reports (2017-2025)
The best piece of journalism I have ever read about Putney. And the most positive. Now we tackle traffic jams.