{
  "title": "The London Grime Index 2026",
  "version": "1.0",
  "published": "2026-09-22",
  "method": {
    "formula": "score = 100 * (w_pm*PM25_n + w_no2*NO2_n + w_den*DEN_n); each *_n is min-max scaled across the 33 boroughs (0 = lowest, 1 = highest)",
    "default_weights": {
      "pm25": 0.45,
      "no2": 0.3,
      "density": 0.25
    },
    "tier_thresholds": {
      "Highest": 60,
      "High": 40,
      "Moderate": 20,
      "Lowest": 0
    },
    "who_2021_guidelines_ugm3": {
      "pm25": 5,
      "no2": 10
    },
    "who_interim_no2_target_ugm3": 20,
    "uk_legal_limits_ugm3": {
      "pm25": 20,
      "no2": 40
    },
    "sensitivity_scenarios": {
      "Published": [
        45,
        30,
        25
      ],
      "Equal thirds": [
        33.3,
        33.3,
        33.3
      ],
      "Air only": [
        60,
        40,
        0
      ],
      "PM2.5 only": [
        100,
        0,
        0
      ],
      "NO2 only": [
        0,
        100,
        0
      ],
      "Density-heavy": [
        30,
        20,
        50
      ]
    },
    "stability": "Same ten boroughs are the top ten in all six scenarios; Havering and Bromley are 33rd and 32nd in all six."
  },
  "sources": {
    "pollution": "Imperial College London ERG for TfL/GLA (June 2026), London health burden of recent air pollution, Table 7: 2024 modelled population-weighted annual means. https://files.localgov.co.uk/imperial.pdf",
    "density": "ONS Census 2021 usual residents per km2, compiled by Vivid Maps: https://vividmaps.com/london-housing-density-map/",
    "context": "Defra (2025) Air Pollution in the UK 2024: Compliance Assessment Summary; London-wide 2019 to 2024 change: PM2.5 10.9 to 7.8 (-28%), NO2 28.8 to 17.0 (-41%)."
  },
  "caveats": [
    "Modelled, not measured, borough averages based on provisional 2024 emissions data.",
    "Index ranks modelled pressure that drives soiling; it does not measure dirt on buildings and is not a health ranking.",
    "Resident density understates commercial building stock (notably City of London).",
    "Scores are relative: 0 means lowest of 33, not clean."
  ],
  "boroughs": [
    {
      "borough": "City of London",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 9.17,
      "no2_2024_ugm3": 24.77,
      "residents_per_km2_census2021": 2971,
      "grime_score": 76.4,
      "rank": 1,
      "tier": "Highest",
      "pm25_rank": 1,
      "no2_rank": 1,
      "pm25_x_who_guideline": 1.83,
      "no2_x_who_guideline": 2.48,
      "local_hook": "Highest PM2.5 and NO2 of any borough; low resident density, far higher daytime population."
    },
    {
      "borough": "Tower Hamlets",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.41,
      "no2_2024_ugm3": 20.82,
      "residents_per_km2_census2021": 15802,
      "grime_score": 75.0,
      "rank": 2,
      "tier": "Highest",
      "pm25_rank": 5,
      "no2_rank": 6,
      "pm25_x_who_guideline": 1.68,
      "no2_x_who_guideline": 2.08,
      "local_hook": "London's most densely populated borough (15,802 residents per km2), which lifts it above boroughs with slightly higher pollution."
    },
    {
      "borough": "Islington",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.43,
      "no2_2024_ugm3": 20.91,
      "residents_per_km2_census2021": 14512,
      "grime_score": 73.3,
      "rank": 3,
      "tier": "Highest",
      "pm25_rank": 4,
      "no2_rank": 5,
      "pm25_x_who_guideline": 1.69,
      "no2_x_who_guideline": 2.09,
      "local_hook": null
    },
    {
      "borough": "Westminster",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.66,
      "no2_2024_ugm3": 21.99,
      "residents_per_km2_census2021": 9510,
      "grime_score": 71.4,
      "rank": 4,
      "tier": "Highest",
      "pm25_rank": 2,
      "no2_rank": 3,
      "pm25_x_who_guideline": 1.73,
      "no2_x_who_guideline": 2.2,
      "local_hook": "Defra reports London Marylebone Road, in Westminster, as the only English monitoring station above the 10 ug/m3 PM2.5 target in 2024."
    },
    {
      "borough": "Kensington and Chelsea",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.55,
      "no2_2024_ugm3": 21.03,
      "residents_per_km2_census2021": 11832,
      "grime_score": 71.1,
      "rank": 5,
      "tier": "Highest",
      "pm25_rank": 3,
      "no2_rank": 4,
      "pm25_x_who_guideline": 1.71,
      "no2_x_who_guideline": 2.1,
      "local_hook": null
    },
    {
      "borough": "Camden",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.39,
      "no2_2024_ugm3": 22.01,
      "residents_per_km2_census2021": 10069,
      "grime_score": 67.0,
      "rank": 6,
      "tier": "Highest",
      "pm25_rank": 6,
      "no2_rank": 2,
      "pm25_x_who_guideline": 1.68,
      "no2_x_who_guideline": 2.2,
      "local_hook": "2nd of 33 for NO2 but 6th for PM2.5. Imperial researchers link the NO2 pattern to construction machinery, particularly near Regent's Park."
    },
    {
      "borough": "Hackney",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.22,
      "no2_2024_ugm3": 19.44,
      "residents_per_km2_census2021": 13519,
      "grime_score": 63.6,
      "rank": 7,
      "tier": "Highest",
      "pm25_rank": 10,
      "no2_rank": 8,
      "pm25_x_who_guideline": 1.64,
      "no2_x_who_guideline": 1.94,
      "local_hook": null
    },
    {
      "borough": "Southwark",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.32,
      "no2_2024_ugm3": 20.07,
      "residents_per_km2_census2021": 10480,
      "grime_score": 61.6,
      "rank": 8,
      "tier": "Highest",
      "pm25_rank": 7,
      "no2_rank": 7,
      "pm25_x_who_guideline": 1.66,
      "no2_x_who_guideline": 2.01,
      "local_hook": null
    },
    {
      "borough": "Lambeth",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.26,
      "no2_2024_ugm3": 19.12,
      "residents_per_km2_census2021": 11819,
      "grime_score": 60.5,
      "rank": 9,
      "tier": "Highest",
      "pm25_rank": 9,
      "no2_rank": 10,
      "pm25_x_who_guideline": 1.65,
      "no2_x_who_guideline": 1.91,
      "local_hook": null
    },
    {
      "borough": "Hammersmith and Fulham",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.3,
      "no2_2024_ugm3": 19.23,
      "residents_per_km2_census2021": 11131,
      "grime_score": 60.3,
      "rank": 10,
      "tier": "Highest",
      "pm25_rank": 8,
      "no2_rank": 9,
      "pm25_x_who_guideline": 1.66,
      "no2_x_who_guideline": 1.92,
      "local_hook": null
    },
    {
      "borough": "Wandsworth",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 8.04,
      "no2_2024_ugm3": 17.78,
      "residents_per_km2_census2021": 9503,
      "grime_score": 48.6,
      "rank": 11,
      "tier": "High",
      "pm25_rank": 11,
      "no2_rank": 12,
      "pm25_x_who_guideline": 1.61,
      "no2_x_who_guideline": 1.78,
      "local_hook": null
    },
    {
      "borough": "Newham",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 8.01,
      "no2_2024_ugm3": 17.42,
      "residents_per_km2_census2021": 9694,
      "grime_score": 47.4,
      "rank": 12,
      "tier": "High",
      "pm25_rank": 12,
      "no2_rank": 14,
      "pm25_x_who_guideline": 1.6,
      "no2_x_who_guideline": 1.74,
      "local_hook": null
    },
    {
      "borough": "Brent",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.94,
      "no2_2024_ugm3": 17.72,
      "residents_per_km2_census2021": 7804,
      "grime_score": 43.3,
      "rank": 13,
      "tier": "High",
      "pm25_rank": 13,
      "no2_rank": 13,
      "pm25_x_who_guideline": 1.59,
      "no2_x_who_guideline": 1.77,
      "local_hook": null
    },
    {
      "borough": "Haringey",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.86,
      "no2_2024_ugm3": 17.14,
      "residents_per_km2_census2021": 9152,
      "grime_score": 42.7,
      "rank": 14,
      "tier": "High",
      "pm25_rank": 15,
      "no2_rank": 16,
      "pm25_x_who_guideline": 1.57,
      "no2_x_who_guideline": 1.71,
      "local_hook": null
    },
    {
      "borough": "Lewisham",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 7.9,
      "no2_2024_ugm3": 16.77,
      "residents_per_km2_census2021": 8595,
      "grime_score": 41.6,
      "rank": 15,
      "tier": "High",
      "pm25_rank": 14,
      "no2_rank": 17,
      "pm25_x_who_guideline": 1.58,
      "no2_x_who_guideline": 1.68,
      "local_hook": null
    },
    {
      "borough": "Ealing",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.71,
      "no2_2024_ugm3": 17.41,
      "residents_per_km2_census2021": 6422,
      "grime_score": 35.3,
      "rank": 16,
      "tier": "Moderate",
      "pm25_rank": 19,
      "no2_rank": 15,
      "pm25_x_who_guideline": 1.54,
      "no2_x_who_guideline": 1.74,
      "local_hook": null
    },
    {
      "borough": "Waltham Forest",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.75,
      "no2_2024_ugm3": 16.22,
      "residents_per_km2_census2021": 7083,
      "grime_score": 34.4,
      "rank": 17,
      "tier": "Moderate",
      "pm25_rank": 17,
      "no2_rank": 21,
      "pm25_x_who_guideline": 1.55,
      "no2_x_who_guideline": 1.62,
      "local_hook": null
    },
    {
      "borough": "Greenwich",
      "zone_statutory": "Inner",
      "pm25_2024_ugm3": 7.79,
      "no2_2024_ugm3": 16.3,
      "residents_per_km2_census2021": 6123,
      "grime_score": 33.7,
      "rank": 18,
      "tier": "Moderate",
      "pm25_rank": 16,
      "no2_rank": 20,
      "pm25_x_who_guideline": 1.56,
      "no2_x_who_guideline": 1.63,
      "local_hook": null
    },
    {
      "borough": "Hounslow",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.6,
      "no2_2024_ugm3": 18.6,
      "residents_per_km2_census2021": 4982,
      "grime_score": 33.3,
      "rank": 19,
      "tier": "Moderate",
      "pm25_rank": 21,
      "no2_rank": 11,
      "pm25_x_who_guideline": 1.52,
      "no2_x_who_guideline": 1.86,
      "local_hook": "11th for NO2 but 21st for PM2.5. Imperial researchers link the gap to Heathrow Airport and its road and air traffic."
    },
    {
      "borough": "Merton",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.74,
      "no2_2024_ugm3": 15.99,
      "residents_per_km2_census2021": 5573,
      "grime_score": 30.9,
      "rank": 20,
      "tier": "Moderate",
      "pm25_rank": 18,
      "no2_rank": 22,
      "pm25_x_who_guideline": 1.55,
      "no2_x_who_guideline": 1.6,
      "local_hook": null
    },
    {
      "borough": "Barnet",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.58,
      "no2_2024_ugm3": 15.96,
      "residents_per_km2_census2021": 4554,
      "grime_score": 25.7,
      "rank": 21,
      "tier": "Moderate",
      "pm25_rank": 22,
      "no2_rank": 23,
      "pm25_x_who_guideline": 1.52,
      "no2_x_who_guideline": 1.6,
      "local_hook": null
    },
    {
      "borough": "Redbridge",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.55,
      "no2_2024_ugm3": 14.94,
      "residents_per_km2_census2021": 5481,
      "grime_score": 24.3,
      "rank": 22,
      "tier": "Moderate",
      "pm25_rank": 24,
      "no2_rank": 26,
      "pm25_x_who_guideline": 1.51,
      "no2_x_who_guideline": 1.49,
      "local_hook": null
    },
    {
      "borough": "Richmond upon Thames",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.55,
      "no2_2024_ugm3": 16.47,
      "residents_per_km2_census2021": 3416,
      "grime_score": 24.3,
      "rank": 23,
      "tier": "Moderate",
      "pm25_rank": 23,
      "no2_rank": 18,
      "pm25_x_who_guideline": 1.51,
      "no2_x_who_guideline": 1.65,
      "local_hook": null
    },
    {
      "borough": "Croydon",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.63,
      "no2_2024_ugm3": 14.75,
      "residents_per_km2_census2021": 4520,
      "grime_score": 23.7,
      "rank": 24,
      "tier": "Moderate",
      "pm25_rank": 20,
      "no2_rank": 27,
      "pm25_x_who_guideline": 1.53,
      "no2_x_who_guideline": 1.48,
      "local_hook": "20th for PM2.5 but 27th for NO2. Imperial researchers say this may reflect construction dust."
    },
    {
      "borough": "Barking and Dagenham",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.46,
      "no2_2024_ugm3": 14.69,
      "residents_per_km2_census2021": 6063,
      "grime_score": 23.0,
      "rank": 25,
      "tier": "Moderate",
      "pm25_rank": 26,
      "no2_rank": 29,
      "pm25_x_who_guideline": 1.49,
      "no2_x_who_guideline": 1.47,
      "local_hook": null
    },
    {
      "borough": "Enfield",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.53,
      "no2_2024_ugm3": 15.42,
      "residents_per_km2_census2021": 4110,
      "grime_score": 22.6,
      "rank": 26,
      "tier": "Moderate",
      "pm25_rank": 25,
      "no2_rank": 24,
      "pm25_x_who_guideline": 1.51,
      "no2_x_who_guideline": 1.54,
      "local_hook": null
    },
    {
      "borough": "Kingston upon Thames",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.46,
      "no2_2024_ugm3": 15.39,
      "residents_per_km2_census2021": 4767,
      "grime_score": 22.3,
      "rank": 27,
      "tier": "Moderate",
      "pm25_rank": 27,
      "no2_rank": 25,
      "pm25_x_who_guideline": 1.49,
      "no2_x_who_guideline": 1.54,
      "local_hook": null
    },
    {
      "borough": "Sutton",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.44,
      "no2_2024_ugm3": 14.44,
      "residents_per_km2_census2021": 4735,
      "grime_score": 19.5,
      "rank": 28,
      "tier": "Lowest",
      "pm25_rank": 28,
      "no2_rank": 30,
      "pm25_x_who_guideline": 1.49,
      "no2_x_who_guideline": 1.44,
      "local_hook": null
    },
    {
      "borough": "Harrow",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.36,
      "no2_2024_ugm3": 14.74,
      "residents_per_km2_census2021": 5158,
      "grime_score": 19.4,
      "rank": 29,
      "tier": "Lowest",
      "pm25_rank": 29,
      "no2_rank": 28,
      "pm25_x_who_guideline": 1.47,
      "no2_x_who_guideline": 1.47,
      "local_hook": null
    },
    {
      "borough": "Hillingdon",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.25,
      "no2_2024_ugm3": 16.46,
      "residents_per_km2_census2021": 2676,
      "grime_score": 16.8,
      "rank": 30,
      "tier": "Lowest",
      "pm25_rank": 31,
      "no2_rank": 19,
      "pm25_x_who_guideline": 1.45,
      "no2_x_who_guideline": 1.65,
      "local_hook": "19th for NO2 but 31st for PM2.5. Imperial researchers link the gap to Heathrow Airport and its road and air traffic."
    },
    {
      "borough": "Bexley",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.3,
      "no2_2024_ugm3": 13.81,
      "residents_per_km2_census2021": 4077,
      "grime_score": 13.9,
      "rank": 31,
      "tier": "Lowest",
      "pm25_rank": 30,
      "no2_rank": 31,
      "pm25_x_who_guideline": 1.46,
      "no2_x_who_guideline": 1.38,
      "local_hook": null
    },
    {
      "borough": "Bromley",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 7.21,
      "no2_2024_ugm3": 13.24,
      "residents_per_km2_census2021": 2197,
      "grime_score": 7.3,
      "rank": 32,
      "tier": "Lowest",
      "pm25_rank": 32,
      "no2_rank": 32,
      "pm25_x_who_guideline": 1.44,
      "no2_x_who_guideline": 1.32,
      "local_hook": "Second-lowest PM2.5 and NO2 and the lowest resident density of the 33, but still above WHO guidelines."
    },
    {
      "borough": "Havering",
      "zone_statutory": "Outer",
      "pm25_2024_ugm3": 6.95,
      "no2_2024_ugm3": 12.41,
      "residents_per_km2_census2021": 2315,
      "grime_score": 0.2,
      "rank": 33,
      "tier": "Lowest",
      "pm25_rank": 33,
      "no2_rank": 33,
      "pm25_x_who_guideline": 1.39,
      "no2_x_who_guideline": 1.24,
      "local_hook": "Lowest PM2.5 and NO2 of any borough, about half the City's NO2, but still above WHO guidelines."
    }
  ]
}