SmogRank / United States / California / Redwood City
Redwood City, month by month
Redwood City has a measured daily mean on 1,215 days since 1 January 2023. Its worst month was September 2023, at 57 US AQI (12.4 µg/m³), 303rd of 2,176 cities on that month's world ranking. Its cleanest was July 2025, at 18 US AQI (3.2 µg/m³). 2025 averaged 31 US AQI (5.5 µg/m³), against 33 US AQI (5.9 µg/m³) in 2024.
Every month since 2023
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
5 months
| Month | Why |
|---|---|
| Aug 2026 | 17 of 31 days measured; a month needs 22. The others: 14 with under 18 hours of readings or readings that failed our checks. |
| Mar 2024 | 16 of 31 days measured; a month needs 22. The others: 1 missing from OpenAQ's archive, 14 with under 18 hours of readings or readings that failed our checks. |
| Feb 2024 | 16 of 29 days measured; a month needs 21. The others: 1 missing from OpenAQ's archive, 12 with under 18 hours of readings or readings that failed our checks. |
| Apr 2023 | 12 of 30 days measured; a month needs 21. The others: 3 missing from OpenAQ's archive, 15 with under 18 hours of readings or readings that failed our checks. |
| Mar 2023 | 13 of 31 days measured; a month needs 22. The others: 15 missing from OpenAQ's archive, 3 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.
Redwood City's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| September 2023 | 5712.4 µg/m³ | 303rdof 2,176 | California and Oregon, United States, September 2023 |
| December 2023 | 5611.7 µg/m³ | 458thof 2,247 | – |
| November 2023 | 5310.0 µg/m³ | 619thof 2,243 | – |
| July 2023 | 529.9 µg/m³ | 674thof 1,432 | – |
| August 2023 | 509.0 µg/m³ | 777thof 1,980 | – |
| October 2023 | 509.0 µg/m³ | 488thof 2,012 | – |
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.
Redwood City's worst days
| Day | US AQI | Episode |
|---|---|---|
| 20 Sept 2023 | 11842.3 µg/m³ | California and Oregon, United States, September 2023 |
| 21 Sept 2023 | 9633.3 µg/m³ | California and Oregon, United States, September 2023 |
| 22 Sept 2023 | 9231.1 µg/m³ | California and Oregon, United States, September 2023 |
| 19 Sept 2023 | 8627.8 µg/m³ | California and Oregon, United States, September 2023 |
| 30 Aug 2023 | 7823.6 µg/m³ | – |
| 23 Sept 2023 | 7723.0 µg/m³ | California and Oregon, United States, September 2023 |
| 17 Dec 2023 | 7622.6 µg/m³ | – |
| 15 Dec 2023 | 7421.3 µg/m³ | – |
| 11 Dec 2024 | 7320.9 µg/m³ | – |
| 7 Dec 2024 | 7320.8 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, Redwood City, United States, 1 Jan 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/redwood-city/history (accessed 13 Oct 2026).
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.
Redwood City now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-13 02:07 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).