{"version":"ew-v3","masterRows":35672,"annualRows":285376,"primaryYear":2025,"validCounts":{"defra-no2-2022":35672,"defra-no2-2023":35672,"defra-no2-2024":35672,"defra-pm25-2022":35672,"defra-pm25-2023":35672,"defra-pm25-2024":35672,"defra-no2-2025":35672,"defra-pm25-2025":35672},"formula":"sum(road metres × assessed grid concentration) / covered road metres; >=99% of all mapped road metres required","sourceRegisterSha256":"bec32d235661f2ba6fb02b0c18ceb1a2413333abf8d603219eee7bafbeae17b9","weightsSha256":"2b32534f2a8a7ef151928efd12a6867b0b9296201192fbb0cf82e48ecc578b75","weightsWithinHalfMetreOfFrozenLsoaRoadTotals":true,"spatialAudit":"air-spatial-audit.json; a total 0.014142 m of sub-metre self-overlap is lost at grid splitting and retained as uncovered length, not reassigned","modelBreak":"2025 uses CMAQ-Urban; 2022–2024 use PCM. Do not pool levels or interpret changes as a homogeneous time trend. Earlier PCM methods may also change by year.","noOutcomeInputs":true,"interpretation":"Background ambient model estimates weighted to the April 2026 mapped road network, including private/restricted roads; not individual exposure, measured roadside concentrations or a causal crash effect.","temporalUse":"2025 source released 2026-10-09; all years weighted by April 2026 roads. Retrospective contextual analysis only for 2022–2025. No certified historical forecast eligibility.","missingPolicy":"Absent or invalid grid cells excluded; coverage gate preserves all master rows; missing never becomes zero.","licence":"Contains Defra data © Crown copyright, Open Government Licence v3.0."}