SmogRank / United States / California / San Leandro
San Leandro, month by month
San Leandro has a measured daily mean on 1,321 days since 1 January 2023. Its worst month was December 2024, at 52 US AQI (9.6 µg/m³), 944th of 2,616 cities on that month's world ranking. Its cleanest was March 2025, at 22 US AQI (4.0 µg/m³). 2025 averaged 36 US AQI (6.5 µg/m³), against 36 US AQI (6.4 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
2 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. |
| Feb 2024 | 20 of 29 days measured; a month needs 21. The others: 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.
San Leandro's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| December 2024 | 529.6 µg/m³ | 944thof 2,616 | California and Oregon, United States, December 2024 |
| September 2023 | 519.2 µg/m³ | 749thof 2,176 | California and Oregon, United States, September 2023 |
| January 2026 | 519.1 µg/m³ | 1,220thof 2,617 | – |
| December 2025 | 498.8 µg/m³ | 1,614thof 3,006 | – |
| June 2024 | 488.6 µg/m³ | 1,082ndof 2,563 | – |
| June 2025 | 468.2 µg/m³ | 1,787thof 2,508 | – |
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 Leandro's worst days
| Day | US AQI | Episode |
|---|---|---|
| 20 Sept 2023 | 11943.0 µg/m³ | California and Oregon, United States, September 2023 |
| 22 Sept 2023 | 9432.0 µg/m³ | California and Oregon, United States, September 2023 |
| 4 Jul 2024 | 9331.8 µg/m³ | California and Nevada, United States, July 2024 |
| 21 Sept 2023 | 9231.0 µg/m³ | California and Oregon, United States, September 2023 |
| 7 Dec 2024 | 8627.7 µg/m³ | California and Oregon, United States, December 2024 |
| 19 Sept 2023 | 8326.2 µg/m³ | California and Oregon, United States, September 2023 |
| 11 Dec 2024 | 8024.5 µg/m³ | California and Oregon, United States, December 2024 |
| 4 Jul 2025 | 7723.3 µg/m³ | – |
| 30 Aug 2023 | 7622.5 µg/m³ | – |
| 23 Sept 2023 | 7421.4 µg/m³ | California and Oregon, United States, September 2023 |
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 Leandro, 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-leandro/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.
San Leandro now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 22:07 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).