Modesto Air Quality in October
Across 2019–2025, Modesto's October air quality had a median AQI of 56 (Moderate) over 217 monitored days in the Modesto, CA area. 6.9% of October days (15 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 52.1% of days. The cleanest October on record here was 2025 (median AQI 43, 0 days above 100) and the worst was 2020 (median 74, 4 days above 100, peak AQI 173).
- Good: 32.3%
- Moderate: 60.8%
- Unhealthy for Sensitive Groups: 4.1%
- Unhealthy or worse: 2.8%
Extra Protection for Modesto Homes
Air quality in Modesto is moderate (AQI 63), with particle pollution the main concern. A True-HEPA purifier gives sensitive groups — kids, seniors and anyone with asthma or allergies — cleaner air indoors on days like today.
Recommended: Coway AP-1512HH Mighty — True HEPA + carbon · CADR ~246 CFM · rooms up to 361 sq ft
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How is the air in Modesto in October?
Moderate on a typical day: median AQI 56 across 2019–2025, with 6.9% of October days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓32.3% of October days were Good (AQI 0–50), 60.8% Moderate (51–100).
- ✓15 days of 217 reached AQI 101+; the October peak was 177.
- ✓Best October: 2025; worst October: 2020.
Frequently asked questions
What is the air quality like in Modesto in October?▾
Across 2019–2025, the median daily AQI in Modesto in October was 56 (Moderate). 32.3% of days were Good, 60.8% Moderate, and 6.9% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is October a good time for outdoor exercise in Modesto?▾
A typical October day in Modesto is Moderate (median AQI 56): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 14 of October days (6.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Modesto's October air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 52.1% of October days in Modesto. The highest October AQI recorded in 2019–2025 was 177 (Unhealthy), in 2020.
Modesto October air quality, year by year
Modesto October air quality by year (Modesto, CA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 31 | 59 | 1 | 177 | PM2.5 |
| 2020worst | 31 | 74 | 4 | 173 | PM2.5 |
| 2021 | 31 | 57 | 4 | 155 | PM2.5 |
| 2022 | 31 | 55 | 0 | 90 | PM2.5 |
| 2023 | 31 | 55 | 3 | 150 | PM2.5 |
| 2024 | 31 | 52 | 3 | 150 | O3 |
| 2025cleanest | 31 | 43 | 0 | 85 | PM2.5 |
What October air means in Modesto
A typical October day in Modesto is Moderate (median AQI 56): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 14 of October days (6.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
October's median AQI of 56 is in line with Modesto's whole-year median of 54, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median October AQI across every EPA metro area (102,872 metro-days, 2019–2025) is 38, so Modesto runs above the national October norm; 6.9% of its October days topped AQI 100 versus 1.3% nationally (above average).
October is part of Modesto's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Modesto
The latest EPA AirNow observation puts Modesto's AQI at 63 (PM10). The figures above are multi-year month statistics, not today's reading.
View current Modesto air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Modesto, CA), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.