The London Grime IndexPrepared by JTD Pressure Washing. 22 September 2026

The London Grime Index 2026: Ranking London’s Dirtiest Boroughs

London's air is cleaner than it has been in years. It is still not shared equally. We ranked all 33 boroughs by the soot and traffic-fume load their buildings face.

Built from 2024 modelled PM2.5 and NO2 for every borough (Imperial College London for TfL and the GLA) and Census 2021 resident density (ONS). Each tile is a borough, ranked from grimiest to lowest and shaded like weathered stone: the darker the tile, the higher the score.

Download the PDF (412 KB) Download CSV ranking Download JSON data Download Excel workbook
Media kit PNG charts for London-wide outlets, trade titles and every borough, plus a live map embed. Free to use with credit.

These are the charts for publication: ranking tiles, pollutant scatter plots and method graphics, supplied as PNGs in zip files. There is also a live borough map you can embed on another site.

Please credit The London Grime Index 2026 and link back to this page when you use them.

London-wide outlets

For London-wide newsrooms and data desks.

London-wide graphics

All six London-wide graphics: full ranking, City vs Havering, Inner vs Outer London, WHO guidelines, improvement since 2019, and how the index is built.

12 PNGs · 1.8 MB · ZIP

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Dynamic map embed

A live SVG map of all 33 boroughs. Hover for rank, score, PM2.5, NO2 and density. Default colours match this page; you can set a brand colour in the builder.

One script · cached SVG

Go to embed builder

Trade press

Shorter packs aimed at one desk. Air quality, property and housing, and cleaning each get the charts that fit that audience.

Air quality

For air-quality and environment trade press: City vs Havering, WHO guidelines, improvement since 2019, and the method graphic.

8 PNGs · 1.2 MB · ZIP

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Property and housing

For property, landlord and housing trade press: full ranking, Inner vs Outer London and improvement since 2019.

6 PNGs · 915 KB · ZIP

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Cleaning

For cleaning and facilities trade press: full ranking, Inner vs Outer London and the method graphic.

6 PNGs · 1.1 MB · ZIP

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Boroughs

Download all 33 boroughs in one zip, or pick a single local authority. Each borough pack has four PNGs: rank chart and scatter chart, each wide (1600×900) and square (1080×1080).

All 33 boroughs

Every borough graphic in one download: 33 folders, four graphics each (132 images).

132 PNGs · 15 MB · ZIP

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One borough

Choose a local authority for its four charts: rank and scatter, each wide (1600×900) and square (1080×1080).

Download zip

Select a borough, then download the zip.

Select a borough to see its numbers. Scores are relative: the lowest borough is not clean, it is just the lowest of 33.

Hover a borough on the map for its Grime Index details. Colours match the tiles: darker means a higher score.

What we found

The Square Mile is grimiest. Havering is lowest.

The City of London scores 76.4 out of 100. Havering scores 0.2. The gap comes from the air itself: modelled 2024 nitrogen dioxide averages 24.8 µg/m³ in the City against 12.4 µg/m³ in Havering, almost exactly double. Fine particles (PM2.5) are 32% higher in the City, at 9.17 against 6.95 µg/m³.

Packed streets push Tower Hamlets and Islington into the top three

Tower Hamlets is London's most densely populated borough, with 15,802 residents per square kilometre, and Islington is second on 14,512. Both also rank in the top five for PM2.5. That combination puts Tower Hamlets second overall and Islington third. Give density the heaviest weight and Tower Hamlets moves to first.

The eleven grimiest boroughs are all Inner London

Behind the City, Tower Hamlets and Islington come Westminster, Kensington and Chelsea, Camden, Hackney, Southwark, Lambeth and Hammersmith and Fulham, with Wandsworth 11th. Newham, at 12th, is the first borough outside statutory Inner London. Taking a simple average of borough figures, Inner London boroughs carry 28% more NO2 (20.0 against 15.7 µg/m³) and 11% more PM2.5 (8.3 against 7.5 µg/m³) than Outer London boroughs.

Seven boroughs are still above the WHO's NO2 interim target

The City of London, Camden, Westminster, Kensington and Chelsea, Islington, Tower Hamlets and Southwark all average above 20 µg/m³ for NO2, the WHO's interim target. The other 26 boroughs are below it.

Heathrow, construction machinery and building dust reorder the table

Hillingdon is 31st for PM2.5 but 19th for NO2. Hounslow is 21st for PM2.5 but 11th for NO2. Imperial College's researchers link that pattern to Heathrow Airport and its road and air traffic. Camden ranks second for NO2 but sixth for PM2.5, which they put down to non-road mobile machinery on construction sites, particularly near Regent's Park. Croydon runs the other way, 20th for PM2.5 and 27th for NO2, a pattern the researchers say may reflect construction dust.

Nowhere is clean by WHO standards. Nowhere is near the legal limits.

Every borough averages above the WHO's 2021 guidelines of 5 µg/m³ for PM2.5 and 10 µg/m³ for NO2. Even Havering is 1.4 times the PM2.5 guideline and 1.2 times the NO2 guideline. No borough average comes close to the UK legal limits of 20 µg/m³ (PM2.5) and 40 µg/m³ (NO2).

Rank every borough

The published index weights PM2.5 at 45%, NO2 at 30% and density at 25%. Change the sliders to test your own view. The ranking barely moves: the same ten boroughs make the top ten under every weighting we tested.

Try a preset:
Show:
Borough ranking under your chosen weights. Click a column heading to sort.
Tier

The small figure under each rank shows movement against the published index. Tiers use the headline score: 60 and above is Highest, 40 to 59 High, 20 to 39 Moderate, below 20 Lowest.

Two pollutants, two stories

PM2.5 and NO2 track each other closely across London (a correlation of 0.95 between boroughs), so most boroughs sit on one diagonal. The exceptions are the interesting part. Bubble size shows resident density.

Scatter chart of modelled 2024 NO2 against PM2.5 for each London boroughMost boroughs lie along a rising diagonal. Hillingdon and Hounslow sit far to the right of that line for their PM2.5 level, reflecting Heathrow. The City of London is top right; Havering is bottom left.
Statutory Inner LondonOuter LondonDashed line: WHO interim NO2 target (20 µg/m³)

London's air is improving

Between 2019 and 2024, London's population-weighted PM2.5 fell 28%, from 10.9 to 7.8 µg/m³, and NO2 fell 41%, from 28.8 to 17.0 µg/m³ (Imperial College London for TfL and the GLA). In 2024, the Greater London zone met the legal annual limit for NO2 for the first time, according to Defra's compliance assessment.

So this index is about the gap between boroughs, not a claim that London is getting dirtier. The ranking shows where the remaining load falls hardest, and which buildings are still taking it.

Find your borough

Pick a borough for a ready-to-use summary with its rank, score and figures. Journalists and councils are welcome to quote it with credit.

How we built it

Grime score = 100 × (0.45 × PM2.5 + 0.30 × NO2 + 0.25 × density)

Each of the three inputs is scaled from 0 (lowest of the 33 boroughs) to 1 (highest) before weighting, so the score is relative rather than absolute.

Why these inputs
Airborne particles, especially the carbon-rich soot from combustion, are the main driver of soiling on stone and other building surfaces, so PM2.5 carries the most weight. NO2 is a marker of traffic and combustion emissions and appears alongside PM10 in standard soiling models. Resident density is a proxy for how many homes and street frontages share the same air.
Where the pollution figures come from
Table 7 of the Imperial College London Environmental Research Group's June 2026 report for Transport for London and the GLA. It gives 2024 modelled, population-weighted annual mean PM2.5 and NO2 for all 33 boroughs, built on the same London Toolkit dispersion modelling that underpins the London Atmospheric Emissions Inventory, at 20 metre resolution. The modelling is a snapshot based on provisional 2024 emissions data.
Why modelled borough averages rather than raw monitor readings
The London Air Quality Network and Defra's UK-AIR stations are essential for checking the model, but they are placed unevenly and mix kerbside and background sites. Averaging the monitors in a borough mostly reflects where the monitors are. Population-weighted modelling covers every borough on the same basis. As a cross-check, Defra's 2024 compliance assessment reports the only English station above the 10 µg/m³ PM2.5 target as London Marylebone Road, in Westminster, and Westminster ranks fourth here.
Where the density figures come from
ONS Census 2021 usual residents per square kilometre. The City of London counts only its roughly 8,600 night-time residents, so its density understates its commercial building stock.
How stable is the ranking?
We re-ran the index under six weightings: the published one, equal thirds, air only, PM2.5 only, NO2 only, and density-heavy. The same ten boroughs are the top ten in all six. Havering and Bromley are 33rd and 32nd in all six. Individual places inside the top ten move by a few positions, so treat ranks within a few points of each other as a tie.

What this index is not

  • It does not measure dirt on walls. It ranks the modelled pressure that drives soiling.
  • It does not score PM10, black carbon, construction dust, wood burning, rainfall, building materials or building age, none of which are published consistently at borough level.
  • It ranks borough averages. Street-level conditions vary sharply inside every borough, and a borough's rank says nothing about a particular building.
  • It is not a health ranking. Health burden depends on age, baseline mortality and deprivation as well as pollution. Imperial's own analysis finds Bexley, Havering and Sutton have among the highest per-person burdens despite lower pollution.

Sources

  1. Dajnak D, Lee S, Stewart G, Holland M, Beevers S, Evangelopoulos D (2026). London health burden of recent air pollution, Table 7. Environmental Research Group, Imperial College London, for TfL and the GLA. files.localgov.co.uk/imperial.pdf. Summary: london.gov.uk/aqmortality.
  2. Office for National Statistics, Census 2021, usual residents per square kilometre by local authority, as compiled by Vivid Maps: vividmaps.com/london-housing-density-map. Original data: ons.gov.uk/census.
  3. Defra (2025). Air Pollution in the UK 2024: Compliance Assessment Summary. UK-AIR. Also reported by Air Quality News.
  4. GLA and TfL (2026). London Atmospheric Emissions Inventory 2022 Summary Note, May 2026. London Datastore.
  5. London Air Quality Network (Imperial College London): londonair.org.uk. Defra UK-AIR: uk-air.defra.gov.uk.
  6. World Health Organization (2021). Global air quality guidelines. who.int.
  7. Soiling evidence: Comite V. et al. (2020), Science of the Total Environment, particulate matter and stone darkening in Florence; Newby P.T. et al. (1991), sources and economic implications of building soiling in urban areas.
  8. Borough map adapted from London-boroughs.svg by Notscott, TUBS and Cmglee, CC BY-SA 3.0. Changes: simplified paths, removed decorative layers, and recoloured boroughs by Grime Index score.

Use this data

The full dataset (JSON), CSV ranking and live scoring workbook (Excel, weights editable) are free to download. The six-way sensitivity test is the sliders and presets in Rank every borough. Please credit and link when you publish.

Suggested credit: The London Grime Index 2026, JTD Pressure Washing, using 2024 modelled air pollution from Imperial College London for TfL and the GLA and Census 2021 data from the Office for National Statistics. https://jtdpressurewashing.co.uk/london-grime-index

Media enquiries: media@jtdpressurewashing.co.uk.

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Add this map to your site

The map is a small embed: one script and a cached SVG. By default it uses the same stone colours as the tiles on this page. Pick a brand colour and the boroughs keep that hue, with darker depth for higher Grime Index scores.

Hover a borough in the preview for rank, score, PM2.5, NO2 and density. Copy the snippet onto any page.