SmogRank / United Kingdom / Wales / Cwmafan

Cwmafan, month by month

Cwmafan has a measured daily mean on 779 days since 1 January 2023. Its worst month was August 2024, at 55 US AQI (11.5 µg/m³), 391st of 2,010 cities on that month's world ranking. Its cleanest was September 2025, at 18 US AQI (3.2 µg/m³).

Every month since 2023

2026too few days for a mean (a year needs 200)83 days measured
Jan24#2,458Feb25#2,658Mar43#2,195AprnoneMaynoneJunnoneJulnoneAugnoneSepnoneOct19#2,627
2025too few days for a mean (a year needs 256)225 days measured
JannoneFebnoneMar2 daysApr42#1,890May37#1,706Jun31#2,233Jul31#2,452Aug29#2,649Sep18#3,044Oct24#2,280Nov9 daysDec29#2,628
202443 for the year258 days measured1,191st of 2,097 in the world
Jan47#1,147Feb41#1,367Mar39#990Apr20 daysMay51#906Jun52#723Jul41#1,572Aug55#391Sep33#1,507Oct21#1,946NovnoneDecnone
2023too few days for a mean (a year needs 256)213 days measured
Jan19 daysFeb3 daysMar11 daysApr54#338May18 daysJun18 daysJul19 daysAug16 daysSep20 daysOct16 daysNov32#1,805Dec41#1,434
Each square is a month's mean PM2.5 in US AQI from Cwmafan's measured days, with its place on that month's world ranking under it. A month has a mean once 70% of its days are measured, the rule the monthly rankings use; under that, the square gives the days measured. Each square opens that month's ranking with Cwmafan marked; each year, the year's. A dashed square is the running month, so far.
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales

Months without a mean, and why

22 months
MonthWhy
Sep 2026No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks.
Aug 2026No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Jul 2026No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Jun 2026No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks.
May 2026No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Apr 2026No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks.
Nov 20259 of 30 days measured; a month needs 21. The others: 21 with under 18 hours of readings or readings that failed our checks.
Mar 20252 of 31 days measured; a month needs 22. The others: 29 with under 18 hours of readings or readings that failed our checks.
Feb 2025No day measured. The others: 28 with under 18 hours of readings or readings that failed our checks.
Jan 2025No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Dec 2024No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Nov 2024No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks.
Apr 202420 of 30 days measured; a month needs 21. The others: 10 with under 18 hours of readings or readings that failed our checks.
Oct 202316 of 31 days measured; a month needs 22. The others: 15 with under 18 hours of readings or readings that failed our checks.
Sep 202320 of 30 days measured; a month needs 21. The others: 10 with under 18 hours of readings or readings that failed our checks.
Aug 202316 of 31 days measured; a month needs 22. The others: 15 with under 18 hours of readings or readings that failed our checks.
Jul 202319 of 31 days measured; a month needs 22. The others: 1 missing from OpenAQ's archive, 11 with under 18 hours of readings or readings that failed our checks.
Jun 202318 of 30 days measured; a month needs 21. The others: 12 with under 18 hours of readings or readings that failed our checks.
May 202318 of 31 days measured; a month needs 22. The others: 13 with under 18 hours of readings or readings that failed our checks.
Mar 202311 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive.
Feb 20233 of 28 days measured; a month needs 20. The others: 25 missing from OpenAQ's archive.
Jan 202319 of 31 days measured; a month needs 22. The others: 6 missing from OpenAQ's archive, 6 with under 18 hours of readings or readings that failed our checks.

A day counts once 18 hours of it are measured; a month needs 70% of its days.

Cwmafan's worst months

MonthUS AQIDays measuredWorld rank
August 2024 5511.5 µg/m³24 of 31391stof 2,010
April 2023 5410.8 µg/m³21 of 30338thof 1,622
June 2024 529.7 µg/m³30 of 30723rdof 2,563
May 2024 519.3 µg/m³31 of 31906thof 2,684
January 2024 478.4 µg/m³29 of 311,147thof 2,385
March 2026 437.8 µg/m³25 of 312,195thof 2,971

Monthly means over the days measured; finished months only. World rank: its place on that month's world ranking of every city with enough days. Each month opens that ranking.

Cwmafan's worst days

DayUS AQI
1 Jun 2024 10135.6 µg/m³
2 Jun 2024 9030.2 µg/m³
13 Jun 2023 8024.4 µg/m³
19 Aug 2024 7723.1 µg/m³
9 Sept 2023 7722.9 µg/m³
14 Feb 2023 7522.0 µg/m³
6 Feb 2024 7320.9 µg/m³
25 Jan 2023 7220.4 µg/m³
12 May 2024 7220.3 µg/m³
15 Feb 2023 7120.1 µg/m³

Daily means, the highest since 1 Jan 2023; the WHO's daily guideline is 15 µg/m³. Each date opens that day's world ranking, and each episode the bad-air spell it was part of.

Use this history

SmogRank, PM2.5 monthly and daily means, Cwmafan, United Kingdom, 1 Jan 2023 – 12 Oct 2026. Monitor data from UK-AIR (Defra), read from the publisher; sources listed at smogrank.com/sources. smogrank.com/gb/cwmafan/history (accessed 13 Oct 2026).

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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.

Cwmafan now: the last 24 hours, its ranks today and the last 12 months day by day.

Updated 2026-10-13 01:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some low-cost readings: Sensor.Community, ODbL (data and licence). Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published (why we use them).