SmogRank / United States / California / Grass Valley
Grass Valley, month by month
Grass Valley has a measured daily mean on 917 days since 1 January 2023. Its worst month was June 2023, at 43 US AQI (7.7 µg/m³), 1,147th of 1,603 cities on that month's world ranking. Its cleanest was January 2024, at 19 US AQI (3.5 µg/m³). 2025 averaged 31 US AQI (5.5 µg/m³), against 27 US AQI (4.9 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
15 months
| Month | Why |
|---|---|
| Oct 2026 | No day measured. |
| Sep 2026 | No day measured. |
| Aug 2026 | No day measured. |
| Jul 2026 | No day measured. |
| Jun 2026 | No day measured. |
| May 2026 | No day measured. |
| Apr 2026 | No day measured. |
| Mar 2026 | No day measured. |
| Feb 2026 | No day measured. |
| Jan 2026 | No day measured. |
| Dec 2025 | No day measured. The others: 31 with no readings from the monitor. |
| Nov 2025 | No day measured. The others: 30 with no readings from the monitor. |
| Oct 2025 | No day measured. The others: 30 with no readings from the monitor, 1 with readings for part of the day (a day needs 18 hours). |
| Mar 2023 | 11 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive. |
| Feb 2023 | 1 of 28 days measured; a month needs 20. The others: 2 with readings for part of the day (a day needs 18 hours), 25 missing from OpenAQ's archive. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Grass Valley's worst months
| Month | US AQI | World rank |
|---|---|---|
| June 2023 | 437.7 µg/m³ | 1,147thof 1,603 |
| July 2024 | 427.5 µg/m³ | 1,533rdof 2,566 |
| July 2025 | 407.2 µg/m³ | 1,952ndof 2,889 |
| May 2023 | 386.9 µg/m³ | 1,157thof 1,600 |
| June 2025 | 376.7 µg/m³ | 2,057thof 2,508 |
| August 2024 | 376.6 µg/m³ | 1,634thof 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.
Grass Valley's worst days
| Day | US AQI |
|---|---|
| 31 Jul 2024 | 8024.6 µg/m³ |
| 9 Aug 2024 | 8024.6 µg/m³ |
| 8 Aug 2024 | 7220.5 µg/m³ |
| 12 Jul 2025 | 6818.2 µg/m³ |
| 30 Jan 2025 | 6516.7 µg/m³ |
| 29 May 2025 | 6516.5 µg/m³ |
| 23 Sept 2023 | 6416.3 µg/m³ |
| 13 Jul 2025 | 6416.3 µg/m³ |
| 1 Aug 2024 | 6315.7 µg/m³ |
| 31 Aug 2023 | 6315.6 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, Grass Valley, 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/grass-valley/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.
Grass Valley 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).