Modesto Air Quality in Fall
Across 2019–2025, Modesto's fall (September–November) air quality had a median AQI of 58 (Moderate) over 637 monitored days in the Modesto, CA area. 8.8% of fall days (56 of 637) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 55.4% of days. The cleanest fall on record here was 2025 (median AQI 52, 1 day above 100) and the worst was 2020 (median 74, 20 days above 100, peak AQI 195).
- Good: 30.8%
- Moderate: 60.4%
- Unhealthy for Sensitive Groups: 6.6%
- Unhealthy or worse: 2.2%
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 fall?
Moderate on a typical day: median AQI 58 across 2019–2025, with 8.8% of fall days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓30.8% of fall days were Good (AQI 0–50), 60.4% Moderate (51–100).
- ✓56 days of 637 reached AQI 101+; the fall peak was 195.
- ✓Cleanest month: November; worst month: September.
Frequently asked questions
What is the air quality like in Modesto in fall?▾
Across 2019–2025, the median daily AQI in Modesto in fall was 58 (Moderate). 30.8% of days were Good, 60.4% Moderate, and 8.8% reached Unhealthy for Sensitive Groups or worse, based on 637 monitored days in EPA's Air Quality System.
Is fall a good time for outdoor exercise in Modesto?▾
A typical fall day in Modesto is Moderate (median AQI 58): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 11 of fall days (8.8%) 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 fall air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 55.4% of fall days in Modesto. The highest fall AQI recorded in 2019–2025 was 195 (Unhealthy), in 2020.
Modesto fall air quality, year by year
Modesto fall air quality by year (Modesto, CA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 91 | 59 | 5 | 177 | PM2.5 |
| 2020worst | 91 | 74 | 20 | 195 | PM2.5 |
| 2021 | 91 | 64 | 12 | 155 | PM2.5 |
| 2022 | 91 | 56 | 9 | 166 | PM2.5 |
| 2023 | 91 | 57 | 3 | 150 | PM2.5 |
| 2024 | 91 | 51 | 6 | 150 | O3 |
| 2025cleanest | 91 | 52 | 1 | 108 | O3 |
What fall air means in Modesto
A typical fall day in Modesto is Moderate (median AQI 58): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 11 of fall days (8.8%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Fall's median AQI of 58 is above Modesto's whole-year median of 54, making it one of the area's dirtier periods. Nationally, the median Fall AQI across every EPA metro area (296,275 metro-days, 2019–2025) is 40, so Modesto runs above the national Fall norm; 8.8% of its Fall days topped AQI 100 versus 1.5% nationally (above average).
Within the season, November is the cleanest month (median AQI 65, 4.8% of days above 100) and September the worst (median 57, 14.8% above 100).
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 season 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.