SmogRank / United States / California / San Francisco
San Francisco, month by month
San Francisco has a measured daily mean on 1,188 days since 1 January 2023. Its worst month was January 2026, at 55 US AQI (11.5 µg/m³), 959th of 2,617 cities on that month's world ranking. Its cleanest was July 2025, at 20 US AQI (3.6 µg/m³). 2025 averaged 38 US AQI (6.9 µg/m³), against 35 US AQI (6.3 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
7 months
| Month | Why |
|---|---|
| Nov 2025 | 18 of 30 days measured; a month needs 21. The others: 12 with under 18 hours of readings or readings that failed our checks. |
| Oct 2024 | 21 of 31 days measured; a month needs 22. The others: 10 with under 18 hours of readings or readings that failed our checks. |
| Sep 2024 | 4 of 30 days measured; a month needs 21. The others: 26 with under 18 hours of readings or readings that failed our checks. |
| Aug 2024 | 13 of 31 days measured; a month needs 22. The others: 18 with under 18 hours of readings or readings that failed our checks. |
| Oct 2023 | 20 of 31 days measured; a month needs 22. The others: 11 with under 18 hours of readings or readings that failed our checks. |
| Sep 2023 | 16 of 30 days measured; a month needs 21. The others: 14 with under 18 hours of readings or readings that failed our checks. |
| Aug 2023 | 7 of 31 days measured; a month needs 22. The others: 24 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.
San Francisco's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| January 2026 | 5511.5 µg/m³ | 959thof 2,617 | – |
| December 2025 | 5511.4 µg/m³ | 1,056thof 3,006 | – |
| December 2024 | 5310.0 µg/m³ | 888thof 2,616 | California and Oregon, United States, December 2024 |
| March 2026 | 498.9 µg/m³ | 1,903rdof 2,971 | – |
| June 2024 | 488.7 µg/m³ | 1,036thof 2,563 | – |
| December 2023 | 478.4 µg/m³ | 1,141stof 2,247 | – |
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.
San Francisco's worst days
| Day | US AQI | Episode |
|---|---|---|
| 20 Sept 2023 | 12143.8 µg/m³ | California and Oregon, United States, September 2023 |
| 22 Sept 2023 | 9532.8 µg/m³ | California and Oregon, United States, September 2023 |
| 7 Dec 2024 | 9432.2 µg/m³ | California and Oregon, United States, December 2024 |
| 19 Sept 2023 | 9432.1 µg/m³ | California and Oregon, United States, September 2023 |
| 21 Sept 2023 | 8829.2 µg/m³ | California and Oregon, United States, September 2023 |
| 23 Sept 2023 | 7823.7 µg/m³ | California and Oregon, United States, September 2023 |
| 8 Dec 2024 | 7823.5 µg/m³ | California and Oregon, United States, December 2024 |
| 15 Jan 2026 | 7723.1 µg/m³ | – |
| 5 Dec 2025 | 7622.3 µg/m³ | – |
| 5 Feb 2026 | 7421.5 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, San Francisco, 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/san-francisco/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.
San Francisco 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).