SmogRank / United States / California / Palo Alto
Palo Alto, month by month
Palo Alto has a measured daily mean on 713 days since 30 August 2024. Its worst month was December 2025, at 62 US AQI (14.9 µg/m³), 733rd of 3,006 cities on that month's world ranking. Its cleanest was April 2026, at 10 US AQI (1.8 µg/m³).
Every month since 2024
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
4 months
| Month | Why |
|---|---|
| Feb 2025 | 17 of 28 days measured; a month needs 20. The others: 11 with under 18 hours of readings or readings that failed our checks. |
| Jan 2025 | 9 of 31 days measured; a month needs 22. The others: 22 with under 18 hours of readings or readings that failed our checks. |
| Sep 2024 | 10 of 30 days measured; a month needs 21. The others: 20 with under 18 hours of readings or readings that failed our checks. |
| Aug 2024 | 1 of 31 days measured; a month needs 22. The others: 1 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.
Palo Alto's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| December 2025 | 6214.9 µg/m³ | 733rdof 3,006 | California, United States, December 2025 |
| December 2024 | 5913.5 µg/m³ | 563rdof 2,616 | California, United States, December 2024 California and Oregon, United States, December 2024 |
| January 2026 | 5511.1 µg/m³ | 985thof 2,617 | California, United States, 30 January to 6 February 2026 California, United States, 26 to 27 January 2026 |
| November 2025 | 529.6 µg/m³ | 1,120thof 2,715 | – |
| February 2026 | 366.5 µg/m³ | 2,340thof 2,866 | California, United States, 30 January to 6 February 2026 |
| September 2025 | 315.6 µg/m³ | 2,285thof 3,104 | – |
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.
Palo Alto's worst days
| Day | US AQI | Episode |
|---|---|---|
| 11 Dec 2024 | 11641.6 µg/m³ | California and Oregon, United States, December 2024 |
| 28 Nov 2025 | 10737.9 µg/m³ | – |
| 20 Dec 2024 | 10236.1 µg/m³ | California, United States, December 2024 |
| 31 Jan 2026 | 10135.6 µg/m³ | California, United States, 30 January to 6 February 2026 |
| 6 Dec 2025 | 9432.2 µg/m³ | California, United States, December 2025 |
| 7 Dec 2024 | 9331.5 µg/m³ | California and Oregon, United States, December 2024 |
| 14 Dec 2025 | 9231.1 µg/m³ | – |
| 7 Dec 2025 | 9230.9 µg/m³ | – |
| 5 Feb 2026 | 9230.9 µg/m³ | California, United States, 30 January to 6 February 2026 |
| 9 Dec 2025 | 8929.5 µg/m³ | – |
Daily means, the highest since 30 Aug 2024; 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, Palo Alto, United States, 30 Aug 2024 – 11 Oct 2026. Monitor data from Clarity and AirGradient via OpenAQ; sources listed at smogrank.com/sources. smogrank.com/us/palo-alto/history (accessed 12 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.
Palo Alto 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).