SmogRank / United States / California / Gridley
Gridley, month by month
Gridley has a measured daily mean on 1,143 days since 7 May 2023. Its worst month was November 2023, at 58 US AQI (12.6 µg/m³), 251st of 2,243 cities on that month's world ranking. Its cleanest was March 2024, at 18 US AQI (3.2 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
6 months
| Month | Why |
|---|---|
| May 2026 | 21 of 31 days measured; a month needs 22. The others: 6 with no readings from the monitor, 4 with readings for part of the day (a day needs 18 hours). |
| Nov 2025 | 14 of 30 days measured; a month needs 21. The others: 6 with no readings from the monitor, 10 with readings for part of the day (a day needs 18 hours). |
| Dec 2024 | 19 of 31 days measured; a month needs 22. The others: 6 with no readings from the monitor, 6 with readings for part of the day (a day needs 18 hours). |
| Jan 2024 | 8 of 31 days measured; a month needs 22. The others: 19 with no readings from the monitor, 4 with readings for part of the day (a day needs 18 hours). |
| Dec 2023 | 20 of 31 days measured; a month needs 22. The others: 9 with no readings from the monitor, 2 with readings for part of the day (a day needs 18 hours). |
| May 2023 | 21 of 31 days measured; a month needs 22. The others: 2 with no readings from the monitor, 2 with readings for part of the day (a day needs 18 hours). |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Gridley's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| November 2023 | 5812.6 µg/m³ | 251stof 2,243 | – |
| January 2026 | 5611.7 µg/m³ | 950thof 2,617 | California, United States, 26 to 27 January 2026 California and Oregon, United States, January 2026 |
| January 2025 | 5310.3 µg/m³ | 940thof 2,474 | – |
| August 2023 | 529.9 µg/m³ | 636thof 1,980 | North-western United States and Canada, August 2023 |
| July 2023 | 519.2 µg/m³ | 736thof 1,432 | – |
| August 2024 | 468.2 µg/m³ | 1,163rdof 2,010 | – |
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.
Gridley's worst days
| Day | US AQI | Episode |
|---|---|---|
| 10 Dec 2023 | 9633.2 µg/m³ | – |
| 30 Aug 2023 | 9231.3 µg/m³ | North-western United States and Canada, August 2023 |
| 14 Nov 2023 | 9030.1 µg/m³ | – |
| 17 Dec 2023 | 8728.4 µg/m³ | California and Oregon, United States, December 2023 |
| 11 Dec 2023 | 8628.0 µg/m³ | – |
| 27 Jan 2026 | 8426.8 µg/m³ | California, United States, 26 to 27 January 2026 |
| 29 Aug 2023 | 8326.3 µg/m³ | North-western United States and Canada, August 2023 |
| 14 Jan 2026 | 8326.2 µg/m³ | California and Oregon, United States, January 2026 |
| 13 Jan 2026 | 8024.7 µg/m³ | California and Oregon, United States, January 2026 |
| 16 Dec 2023 | 8024.6 µg/m³ | California and Oregon, United States, December 2023 |
Daily means, the highest since 7 May 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, Gridley, United States, 7 May 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/gridley/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.
Gridley now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 17:07 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).