SmogRank / United States / California / Chico
Chico, month by month
Chico has a measured daily mean on 1,292 days since 1 January 2023. Its worst month was January 2026, at 58 US AQI (12.8 µg/m³), 886th of 2,617 cities on that month's world ranking. Its cleanest was March 2024, at 15 US AQI (2.7 µg/m³). 2025 averaged 44 US AQI (7.9 µg/m³), against 39 US AQI (7.1 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
1 month
| Month | Why |
|---|---|
| Jan 2025 | 15 of 31 days measured; a month needs 22. The others: 16 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.
Chico's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| January 2026 | 5812.8 µg/m³ | 886thof 2,617 | California and Oregon, United States, January 2026 |
| November 2023 | 5812.7 µg/m³ | 243rdof 2,243 | – |
| December 2023 | 5712.4 µg/m³ | 407thof 2,247 | Western United States and Mexico, December 2023 California and Oregon, United States, December 2023 |
| December 2024 | 5712.4 µg/m³ | 635thof 2,616 | California and Oregon, United States, December 2024 |
| August 2024 | 5611.6 µg/m³ | 379thof 2,010 | North-western United States and Canada, August 2024 |
| February 2025 | 5511.3 µg/m³ | 1,073rdof 2,633 | Western United States and Mexico, January and February 2025 |
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.
Chico's worst days
| Day | US AQI | Episode |
|---|---|---|
| 2 Aug 2024 | 16981.2 µg/m³ | North-western United States and Canada, August 2024 |
| 30 Jan 2025 | 9633.3 µg/m³ | Western United States and Mexico, January and February 2025 |
| 29 Aug 2023 | 9432.1 µg/m³ | North-western United States and Canada, August 2023 |
| 1 Aug 2024 | 9331.8 µg/m³ | North-western United States and Canada, August 2024 |
| 28 Nov 2024 | 8929.3 µg/m³ | – |
| 29 Jan 2025 | 8728.5 µg/m³ | Western United States and Mexico, January and February 2025 |
| 7 Dec 2024 | 8728.3 µg/m³ | California and Oregon, United States, December 2024 |
| 12 Nov 2023 | 8628.1 µg/m³ | – |
| 1 Dec 2024 | 8628.1 µg/m³ | California and Oregon, United States, December 2024 |
| 11 Nov 2023 | 8627.7 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, Chico, 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/chico/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.
Chico now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 18:07 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).