SmogRank / United States / California / San Diego
San Diego, month by month
San Diego has a measured daily mean on 1,360 days since 1 January 2023. Its worst month was December 2025, at 62 US AQI (15.2 µg/m³), 720th of 3,006 cities on that month's world ranking. Its cleanest was March 2024, at 38 US AQI (6.9 µg/m³). 2025 averaged 54 US AQI (10.6 µg/m³), against 52 US AQI (9.5 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
San Diego's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| December 2025 | 6215.2 µg/m³ | 720thof 3,006 | Western United States and Mexico, December 2025 |
| December 2024 | 6214.8 µg/m³ | 486thof 2,616 | South-western United States and Mexico, December 2024 to January 2025 California and Oregon, United States, December 2024 |
| April 2023 | 5812.7 µg/m³ | 226thof 1,622 | – |
| December 2023 | 5712.5 µg/m³ | 400thof 2,247 | Western United States and Mexico, December 2023 |
| November 2025 | 5712.5 µg/m³ | 717thof 2,715 | – |
| August 2025 | 5511.5 µg/m³ | 894thof 2,901 | – |
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 Diego's worst days
| Day | US AQI | Episode |
|---|---|---|
| 6 Dec 2024 | 10537.1 µg/m³ | California and Oregon, United States, December 2024 |
| 16 Dec 2025 | 9834.4 µg/m³ | Western United States and Mexico, December 2025 |
| 1 Jan 2025 | 9532.6 µg/m³ | South-western United States and Mexico, December 2024 to January 2025 |
| 14 Dec 2025 | 9432.0 µg/m³ | Western United States and Mexico, December 2025 |
| 17 Dec 2025 | 9331.9 µg/m³ | Western United States and Mexico, December 2025 |
| 13 Dec 2025 | 9231.2 µg/m³ | Western United States and Mexico, December 2025 |
| 5 Dec 2024 | 8929.5 µg/m³ | California and Oregon, United States, December 2024 |
| 29 Dec 2023 | 8627.8 µg/m³ | – |
| 17 May 2026 | 8627.8 µg/m³ | California, United States, May 2026 |
| 25 Jan 2025 | 8527.6 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 Diego, 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-diego/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 Diego now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 19:07 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).