Air Quality in Modesto, California — Live
Live readings from PurpleAir sensors across Modesto — with free alerts the moment the air turns.
AQI 26 from 5 PurpleAir sensors · Trending up · data from PurpleAir
As of , the air quality in Modesto, California is AQI 26 — Good and rising — with PM2.5 at 4.7 µg/m³, the median of 5 live PurpleAir sensors reading 22 to 66. Canairy's verdict: Breathe easy.
For scale, that PM2.5 reading is below the World Health Organization's 24-hour guideline of 15 µg/m³. The WHO figure is a daily average and this is a live reading, so read it as a sense of magnitude rather than a formal exceedance — a brief spike and a bad day are not the same thing. More on the WHO guidelines
Pollen today in Modesto: weeds pollen is the strongest of the three at a low level, from Google's pollen forecast. Canairy shows the tree, grass and weed forecast beside the air reading on every plan, including the free one.
Free to download · Live data from PurpleAir & public monitors
Live PurpleAir sensor map for Modesto and Ceres, Turlock, Riverbank, Oakdale. Every dot is a real sensor, color-coded by current air quality.
Sensor by sensor in Modesto
The sensors Canairy reads in Modesto are 44 AQI points apart right now, from Good to Moderate, which is the whole reason one city-wide number can mislead you: the median describes air you may not be standing in.
| From city center | AQI | Category |
|---|---|---|
| 1.0 mi N | 24 | Good |
| 2.0 mi WNW | 31 | Good |
| 2.1 mi NE | 28 | Good |
| 4.9 mi NW | 22 | Good |
| 6.7 mi ESE | 66 | Moderate |
Modesto sits on the floor of the San Joaquin Valley, one of the hardest air basins in the country to keep clean. The mountains that ring the Valley trap whatever the city and its farms put into the air, so Modesto swings between smoggy, ozone-heavy summers and winters when cold, stagnant air and Tule fog press wood smoke and fine particles down to street level. The Modesto area has landed among the nation's worst metros for particle pollution more than once, and Stanislaus County has earned failing grades from the American Lung Association.
What Canairy does for Modesto
A clear verdict
Not just a number — a plain-English call for Modesto: open the windows, or keep them shut.
Smoke alerts
A push or text the moment the air crosses your threshold — and again when it clears.
A heads-up before it's bad
Trend alerts catch the air turning, so you can close up the house before the smoke settles in.
Every place you care about
Home, work, the kids' school — across Modesto or across the country, on one screen.
What the air in Modesto is doing next
| When | AQI | Expected air quality | Main pollutant |
|---|---|---|---|
| Today | 35 | Good | ozone |
Forecast from EPA AirNow for the Modesto reporting area. Canairy watches the live sensors against it and tells you when the air actually crosses your threshold, rather than leaving you to check.
Why the Valley traps Modesto's air
Modesto sits low on the San Joaquin Valley floor, walled in by the Coast Ranges to the west and the Sierra Nevada to the east. On calm days the mountains keep air from flushing out, so pollution from traffic, farms, and industry lingers instead of blowing away. This is a big part of why San Joaquin Valley metros, Modesto among them, keep showing up near the top of the American Lung Association's worst-air lists, and why all eight Valley counties have carried failing grades.
Winter is when it bites hardest. Cold nights build strong temperature inversions that cap the Valley like a lid, and Tule fog, the dense ground fog unique to the Central Valley, settles in from roughly November through February. Under that lid, fine-particle pollution from cars, fireplaces, and farms has nowhere to go, and PM2.5 readings can climb for days at a time until a storm finally clears the basin.
Everyday sources: farms, Highway 99, and winter wood smoke
Most of Modesto's air story is not wildfire, it is everyday life in a farm city. Stanislaus County is one of California's most productive agricultural counties, and the orchards and fields around town kick up dust, especially during the late-summer and fall almond harvest, when harvesters shake trees and sweep nuts off the ground. The regional air district's low-dust harvester program, launched in 2018, has cut a lot of that dust, but harvest season still shows up in the numbers. Running down the middle of it all is Highway 99, the freight and commuter spine of the Valley, adding a steady load of vehicle exhaust.
In winter, wood smoke becomes the swing factor. Because fireplace and wood-stove smoke is such a large share of cold-weather PM2.5, the San Joaquin Valley Air District runs its Check Before You Burn program from November through February. Each day the District declares whether burning is allowed in your county based on the forecast, and on the worst days all wood burning is banned. Checking that status, or just watching your local sensor, is the simplest way to know whether tonight is a fire night or a keep-the-windows-closed night.
When wildfire smoke reaches Modesto
Modesto is not in the forest, but Valley geography means smoke finds it anyway. In 2020 the SCU Lightning Complex burned across six counties including Stanislaus itself, part of a fire season so severe that the August Complex to the north became the largest wildfire in recorded California history. Smoke from those fires and others drifted over the Central Valley for weeks that autumn, and the same inversions that trap winter pollution can hold wildfire haze in place once it arrives.
Smoke does not settle evenly across town. During the 2020 fires, monitors showed cleaner air in central Modesto while neighborhoods on the north and west sides of Stanislaus County slid into the unhealthy range. That is exactly the kind of block-by-block difference a single official number can hide, and the reason it helps to watch the sensor closest to your own street rather than a citywide average.
Modesto air quality FAQ
What is the air quality in Modesto right now?
As of September 5, 2026 at 5:10 AM PDT, the air quality in Modesto, California is AQI 26 — Good — with PM2.5 at 4.7 µg/m³, the median of 5 live PurpleAir sensors. Open the windows. Great for outdoor activity.
When is Modesto's air quality usually worst?
Modesto has two hard seasons. Summer brings ground-level ozone, the Valley's warm-weather smog, which is often the headline pollutant on hot afternoons. Winter brings fine particles: cold nights build inversions and Tule fog that trap wood smoke, traffic exhaust, and farm dust near the ground, sometimes pushing PM2.5 up for days until a storm clears the basin.
Can I burn wood in my fireplace in Modesto tonight?
It depends on the day. From November through February the San Joaquin Valley Air District runs Check Before You Burn, declaring each day whether wood burning is allowed in Stanislaus County based on the forecast for fine-particle pollution, and banning it outright on the worst days. Check the District's daily status before lighting a fire, and watch your local sensor here to see how the air is actually trending in your neighborhood.
What the AQI numbers mean
| AQI | Category | What it means for you |
|---|---|---|
| 0–50 | Good | Open the windows. Great for outdoor activity. |
| 51–100 | Moderate | Sensitive groups may want to take it slower outside. |
| 101–150 | Unhealthy for Sensitive Groups | Kids, elderly, and respiratory conditions stay closer to home. |
| 151–200 | Unhealthy | Skip outdoor exercise. Close windows. |
| 201–300 | Very Unhealthy | Limit time outside. N95 if you must go. |
| 301+ | Hazardous | Health emergency. Stay inside, run filtration if you have it. |
Canairy lets you tighten these bands if you’re more sensitive than the EPA default, so an alert can fire before the official category changes. How to read the Air Quality Index
Where these readings come from
The AQI at the top of this page is the median of the 5 curated PurpleAir sensors Canairy tracks in and around Modesto, with outliers set aside so that one sensor brought indoors — or parked beside a barbecue — cannot set the number for a whole city. Every sensor behind it is listed above with its distance and bearing from the city center. There is no black box here.
In the app, a place you save resolves the same way first. When no neighborhood sensor is reporting it falls back to the nearest EPA AirNow monitor, and anything modeled rather than measured is labelled a regional estimate rather than passed off as a sensor reading. How low-cost sensors compare to regulatory monitors
About Canairy
Canairy is free to download. The free plan covers one saved place with live readings, a plain-English verdict, and push alerts when the air crosses a threshold you choose. Paid plans add more places, faster refreshes, and SMS alerts. It is built by two parents in Sonoma County, California, who got tired of guessing whether it was safe to send the kids outside. Why we built it
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Air quality near Modesto
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