Is Putney air quality improving?

Yes. Kerbside NO2 on Putney High Street has fallen from approximately 110 µg/m³ in 2015 to about 32 µg/m³ in 2026, finally crossing under the 40 µg/m³ UK legal limit.

Which intervention reduced NO2 the most?

The TfL bus upgrades in 2013 and especially 2023 line up with the biggest step-downs in kerbside NO2. ULEZ phases are visible but smaller in magnitude.

What is the "roadside increment"?

The difference between kerbside (Putney High Street) and the background sites (Putney and Barnes). It isolates how much of the kerbside NO2 is from the road itself versus the urban background.

What is sparse data and why are some markers hollow?

A monitoring site with less than 75% data capture for a year shows a hollow dashed marker. The value is still shown but should not be over-interpreted.

Putney Air Quality

Nitrogen dioxide (NO₂) is produced primarily by vehicle exhaust and serves as an independent proxy for motor traffic volume. The chart below shows annual mean NO₂ at automatic and diffusion-tube sites within 3km of Hammersmith Bridge.

Monitoring sites

WA7 Kerbside, automatic monitor on Putney High Street, 1.75m inlet, about 0.5m from the kerb.
WA8 Facade, automatic monitor on the same building, 4.85m inlet. Decommissioned January 2024.
W24 McDonalds, diffusion tube on Putney High Street outside the McDonald's sign. Continuous monthly sampling.
RI1 Castelnau, automatic roadside on the Barnes approach to Hammersmith Bridge.
WA9 Felsham Road, automatic urban background, about 600m off Putney High Street.
RI2 Barnes Wetlands, automatic suburban background, just west of Hammersmith Bridge.

Reading the chart

The Combine button averages a group's selected sites into a single line. The All and None buttons toggle every pill in a group at once. Toggling between Absolute and Index changes the y-axis. The Baseline dropdown sets the start year of the chart in both views, and also anchors the 100-point in Index view.

Hollow dashed markers are years with low data capture (under 75%). Wandsworth's 2024 Annual Air Quality Status Report flags WA7 and WA9 for 2022 and 2023 as "insufficient valid data".

Reference lines: the UK and Wandsworth annual mean limit of 40 µg/m³, and the WHO 2021 guideline of 10 µg/m³ which Wandsworth adopted as an interim target in September 2023.

Putney HS Roadside Increment

The roadside increment is the difference between roadside NO₂ concentration and urban background NO₂ concentration. It isolates the contribution of local road traffic by subtracting the regional and London-wide component that affects all sites. It is a standard metric in air quality assessment, used by Defra, the LAQN and the AURN to evaluate the local impact of road traffic and of interventions intended to reduce it.

On this chart it is calculated per year as the average of the selected Putney High Street sites (WA7, WA8, W24) minus the average of the selected Putney Background sites (WA9, RI2).

Common questions

Is Putney air quality improving?: Yes. Kerbside NO2 on Putney High Street has fallen from approximately 110 µg/m³ in 2015 to about 32 µg/m³ in 2026, finally crossing under the 40 µg/m³ UK legal limit.
Which intervention reduced NO2 the most?: The TfL bus upgrades in 2013 and especially 2023 line up with the biggest step-downs in kerbside NO2. ULEZ phases are visible but smaller in magnitude.
What is the "roadside increment"?: The difference between kerbside (Putney High Street) and the background sites (Putney and Barnes). It isolates how much of the kerbside NO2 is from the road itself versus the urban background.
What is sparse data and why are some markers hollow?: A monitoring site with less than 75% data capture for a year shows a hollow dashed marker. The value is still shown but should not be over-interpreted.