SmogRank / United Kingdom / Wales / Cardiff

Cardiff, month by month

Cardiff has a measured daily mean on 722 days since 1 January 2023. Its worst month was April 2023, at 59 US AQI (13.4 µg/m³), 200th of 1,622 cities on that month's world ranking. Its cleanest was July 2024, at 27 US AQI (4.8 µg/m³).

Every month since 2023

2026too few days for a mean (a year needs 200)88 days measured
Jan51#1,220Feb48#1,771Mar57#1,124AprnoneMaynoneJunnoneJulnoneAugnoneSep1 dayOct31#1,866
2025too few days for a mean (a year needs 256)179 days measured
JannoneFebnoneMarnoneAprnoneMay21 daysJun39#2,001Jul52#1,283Aug17 daysSep32#2,193Oct18 daysNov12 daysDec51#1,536
2024too few days for a mean (a year needs 257)251 days measured
Jan51#972Feb51#797Mar50#580Apr19 daysMay49#1,054Jun40#1,624Jul27#2,306Aug40#1,489Sep49#611Oct36#1,303NovnoneDecnone
2023too few days for a mean (a year needs 256)204 days measured
Jan15 daysFeb2 daysMar6 daysApr59#200May18 daysJun18 daysJul19 daysAug12 daysSep58#271Oct15 daysNov51#845Dec47#1,105
Each square is a month's mean PM2.5 in US AQI from Cardiff'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 Cardiff 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

25 months
MonthWhy
Sep 20261 of 30 days measured; a month needs 21. The others: 29 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 202512 of 30 days measured; a month needs 21. The others: 18 with under 18 hours of readings or readings that failed our checks.
Oct 202518 of 31 days measured; a month needs 22. The others: 13 with under 18 hours of readings or readings that failed our checks.
Aug 202517 of 31 days measured; a month needs 22. The others: 14 with under 18 hours of readings or readings that failed our checks.
May 202521 of 31 days measured; a month needs 22. The others: 10 with under 18 hours of readings or readings that failed our checks.
Apr 2025No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks.
Mar 2025No day measured. The others: 31 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 202419 of 30 days measured; a month needs 21. The others: 11 with under 18 hours of readings or readings that failed our checks.
Oct 202315 of 31 days measured; a month needs 22. The others: 16 with under 18 hours of readings or readings that failed our checks.
Aug 202312 of 31 days measured; a month needs 22. The others: 19 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 20236 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive, 5 with under 18 hours of readings or readings that failed our checks.
Feb 20232 of 28 days measured; a month needs 20. The others: 25 missing from OpenAQ's archive, 1 with under 18 hours of readings or readings that failed our checks.
Jan 202315 of 31 days measured; a month needs 22. The others: 7 missing from OpenAQ's archive, 9 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.

Cardiff's worst months

MonthUS AQIDays measuredWorld rankEpisode
April 2023 5913.4 µg/m³22 of 30200thof 1,622–
September 2023 5812.8 µg/m³23 of 30271stof 2,176–
March 2026 5712.5 µg/m³25 of 311,124thof 2,971Europe, 18 to 25 March 2026
Europe, 1 to 12 March 2026
July 2025 529.9 µg/m³29 of 311,283rdof 2,889–
January 2024 519.3 µg/m³28 of 31972ndof 2,385–
February 2024 519.2 µg/m³21 of 29797thof 2,486–

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.

Cardiff's worst days

DayUS AQIEpisode
25 Jan 2023 10236.0 µg/m³France, The Netherlands and United Kingdom, January 2023
9 Mar 2026 9432.0 µg/m³Europe, 1 to 12 March 2026
14 Feb 2023 9331.7 µg/m³Europe, 6 to 25 February 2023
11 Jun 2023 8829.0 µg/m³United Kingdom, Belgium and 2 more countries, June 2023
15 Feb 2023 8326.2 µg/m³Europe, 6 to 25 February 2023
21 Mar 2026 8226.0 µg/m³Europe, 18 to 25 March 2026
5 Mar 2026 8225.5 µg/m³Europe, 1 to 12 March 2026
9 Sept 2023 8024.5 µg/m³–
30 Apr 2023 7823.8 µg/m³–
1 Jun 2024 7823.8 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, Cardiff, 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/cardiff/history (accessed 12 Oct 2026).

Download chart (PNG)

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.

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

Updated 2026-10-12 23:07 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).