Modesto Real-Time AQI Tracker
Get Alerts For Unhealthy AQI In Your Area
When air quality in your area reaches unhealthy levels, we'll send you a quick alert, along with expert tips on how to reduce your exposure.
What's Actually In Modesto Air Today?
What High AQI Means for Your Lungs in Modesto
How to Read AQI
The Air Quality Index (AQI) measures how polluted the air is and how it may affect your health.
0–50 (Good): Air quality is satisfactory.
51–100 (Moderate): Acceptable, but some pollutants may pose minor concerns.
101–150 (Unhealthy for Sensitive Groups)
151–200 (Unhealthy)
201–300 (Very Unhealthy)
301+ (Hazardous)
Moderate
Still okay for most, but if you have asthma or allergies, take it easy and avoid long outdoor workouts.
Shop MERV 11 filters→What's the Right Filter for Your AQI Level?
Check Today's Live Real Time Air Quality Index AQI Map in Modesto, CA Now
Why you can trust this page: Filterbuy has made air filters in Talladega, Alabama, for over a decade. An HVAC technician reviewed this guidance, and every statistic links to its source.
TL;DR
The live map on this page shows Modesto's air quality index right now, using EPA AirNow data that refreshes through the day. Under 50 is good for everyone; above 100, sensitive groups should ease off outdoors. Fine particles (PM2.5), the tiny specks in smoke and exhaust, build up under winter inversions, ozone peaks on hot summer afternoons, and wildfire smoke can arrive in any dry month. Filterbuy's action line for indoor steps is AQI 100.
Modesto Air Quality Now: Reading the Live AQI Map
The Modesto AQI map at the top of this page shows current air quality in Modesto in real time. Start with the color: green or yellow is an ordinary day for most people, and orange or higher means sensitive groups should scale back. The pollutant label is almost always PM2.5 or ground-level ozone, and each calls for a different response indoors.
The number is a citywide snapshot. Modesto's main regulatory monitor is the Valley Air District's Modesto–14th Street station downtown, so north Modesto, the Airport District or Highway 99 can read differently in the same hour.
Filterbuy tip: On a bad-air day, check the map in the morning before you open windows, then again around 4 p.m., when ozone usually peaks.
Key Takeaways
Modesto's PM2.5 peaks November through February under valley inversions, while ozone peaks on hot afternoons from late spring through early fall.
Stanislaus County is one of 20 U.S. counties that failed all three State of the Air 2026 measures, ranking 18th worst for ozone.
EPA recommends a MERV 13 or higher filter in a central HVAC system during smoke events. Filterbuy's line for acting on that's AQI 100.
Modesto AQI Levels: What Each Color Means and What to Do
Match the map's color to the row below. Categories and precautions follow EPA AirNow guidance.
Per EPA AirNow guidance.
Since May 6, 2024, EPA's cutoff for Good PM2.5 has been 9.0 micrograms per cubic meter instead of 12.0 (EPA fact sheet), so valley days that once showed green now often show yellow.
Filterbuy's action line is AQI 100. That's still the top of Moderate, and it's where we tell Modesto households to act: MERV 13 in the HVAC, the thermostat fan set to On, a portable HEPA air cleaner in each occupied room (bedrooms first) and the house closed up. Above 200, follow AirNow and local guidance first.
Why Modesto's AQI Can Disagree with the Sky
This map and AirNow show a NowCast AQI, a weighted average of recent hours, so it can lag a fast-moving smoke plume. The Valley Air District's myRAAN reports hourly readings from the same monitors and often moves first (Valley Air District). If you smell smoke while the map still shows yellow, trust your senses and check myRAAN or the AirNow Fire and Smoke Map.
Is the Air Quality Bad in Modesto Today?
It depends on the live number. Below 50 is good for everyone, and 51 to 100 is fine for most people. Above 100, people with asthma, COPD or heart disease, children, older adults and outdoor workers should cut back outside; above 150, everyone should. Ozone builds through the afternoon; winter PM2.5 is usually worst from evening through mid-morning.
If someone at home has asthma, COPD or a heart condition, follow their doctor's plan along with AirNow and Stanislaus County guidance.
What to Do at Each AQI Level in Your Modesto Home
Find your home type, then match the row to the live map.
EPA guidance plus Filterbuy's AQI 100 action line. Never seal up a hot home without a way to cool it.
What's in Modesto's Air, Season by Season
Modesto sits in a mountain-walled valley where stalled air has few ways out. Winter PM2.5 is largely ammonium nitrate, which forms when engine exhaust reacts with farm ammonia (CARB). Ozone breaks down indoors fairly quickly, but PM2.5 lingers, which makes it a filter problem.
Nov–Feb: PM2.5 from inversions, wood smoke and tule fog. Check the daily burn status.
Mar–Apr: Usually the cleanest stretch. Swap in a fresh filter.
May–Sep: Ozone season. Move workouts before 10 a.m. and stock a spare MERV 13.
Jun–Nov: Wildfire smoke can arrive within hours from the Sierra foothills or the Diablo Range.
Modesto Air Quality by Neighborhood
Blocks beside Highway 99, rail lines and truck routes often run higher on fine particles than streets a mile away. For block-level readings, Modesto City Schools has a PurpleAir sensor at each of its 34 campuses (Modesto City Schools), and the SJVAir network runs more than 400 community monitors.
How Does Modesto's Air Quality Rank?
In the American Lung Association's State of the Air 2026 report, Stanislaus County ranks 18th worst for ozone and ties for 19th for year-round particle pollution. Compare nearby cities on our Fresno, Stockton and Sacramento AQI maps.
Wildfire Smoke and Winter Inversions: What to Do
On November 14, 2018, Camp Fire smoke from about 150 miles away pushed local PM2.5 to 146 micrograms per cubic meter (Turlock Journal).
Start with official guidance from AirNow, the Valley Air District and Stanislaus County Public Health. Then, at AQI 100 and above, Filterbuy recommends four steps:
MERV 13 in the HVAC. Your MERV 13 filter is the whole-home layer.
Thermostat fan set to On, so air moves through the filter all the time.
A portable HEPA air cleaner in each occupied room, bedrooms first. HEPA belongs in a portable unit, never the furnace slot (MERV 13 vs. HEPA).
Close the house up. Skip candles, frying, smoking and the fireplace.
During smoke, check the HVAC filter. EPA says to replace it when it looks dirty, dark brown or black, which can be well before the normal interval, and to keep spares on hand (EPA). To track fires, see our Modesto wildfire and smoke map.
Burn Days and Valley Air Advisories
From November through February, the Valley Air District posts a daily wood-burning status for Stanislaus County at valleyair.org/burnstatus and in the Valley Air app. On no-burn days, burning any solid fuel is banned from midnight to midnight (Valley Air District). Treat those days as filtration days: set the fan to On and check the filter.
Modesto Homes Without Central HVAC
Some older Modesto homes and many apartments use swamp coolers, window units or wall heaters. Without ducts, portable HEPA air cleaners in each occupied room are your main defense. Run swamp coolers sparingly on smoky days. The Valley Air District's Clean Air Centers and free Clean Air Rooms purifiers can help.
Choosing a Portable Air Cleaner
Size it to the room. EPA calls for a smoke CADR of at least two-thirds of the room's square footage, so a 300 sq ft bedroom needs about 200 (EPA).
Skip anything that makes ozone. EPA advises against ozone-producing air cleaners, including ionizers.
DIY box-fan cleaners work as a stopgap. Use MERV 13 filters and a certified fan made in 2012 or later, and never leave it running unattended (EPA).
Our Take: What a Filter Maker Reads in Modesto's Air
As a filter maker, Filterbuy sees two things in Modesto's data. First, the city has two filter seasons: winter inversions often last longer than smoke events, so upgrading only when the sky turns orange misses much of the year. Second, summer AC runtimes and harvest dust load filters faster than usual, so we suggest a monthly look from June through October.
Wildfire smoke is the clearest case for why filtration matters. Modesto families cannot control what the Sierra or the Diablo Range sends into the valley, but they can control what their HVAC system removes before it reaches a bedroom. We have been manufacturing filters for over a decade and serving more than two million households, and smoke season is when that work matters most.
David Heacock, Founder & CEO, Filterbuy (first published on our Modesto wildfire and smoke map)
Which Filter Modesto's AQI Calls For
For wildfire smoke, the answer is MERV 13. EPA recommends MERV 13 or higher during smoke events and notes that most HVAC systems can run it without problems when the filter is replaced often (EPA). Filterbuy makes MERV 8, MERV 11 and MERV 13 pleated filters in the USA in 600+ sizes, plus custom air filters. Smoke odor is a gas that pleated filters don't capture; for odors, see our Odor Eliminator line.
Confirm your filter size before ordering, the same as with any tier.
Supporting Statistics
A HEPA room purifier can cut indoor particles by more than 90% in a well-sealed room. Source: Valley Air District
Asthma ER visits ran 17% higher than expected on 2023 wildfire smoke days. Source: CDC, MMWR
Stanislaus County is one of 20 U.S. counties to fail all three State of the Air 2026 measures. Source: American Lung Association
Frequently Asked Questions
What Is the Air Quality in Modesto Today?
The live map above shows Modesto's current AQI and main pollutant, usually PM2.5 in winter or ozone in summer.
Is the Air Quality Bad in Modesto Today?
If the map reads above 100, sensitive groups should cut back outdoors; above 150, everyone should. Under 100, it's fine for most people.
What MERV Rating Do I Need for Wildfire Smoke in Modesto?
MERV 13. EPA recommends MERV 13 or higher in a central HVAC system during smoke events. HEPA belongs in portable room cleaners, not the furnace slot.
What Should I Do When Modesto's AQI Reaches 100?
Filterbuy recommends MERV 13 in the HVAC, the fan set to On, a portable HEPA cleaner in each occupied room and closing the house up. Above 200, follow AirNow and local guidance first.
How Often Should I Change My Air Filter in Modesto?
Filterbuy pleated filters are built for a 90-day service life under typical use. During smoke, EPA says to replace the filter when it looks dark brown or black, which can be sooner.
Glossary
AQI (Air Quality Index): EPA's 0–500 scale, from Good (0–50) to Hazardous (301+).
PM2.5: Fine particles 2.5 micrometers or smaller, found in smoke and exhaust.
Inversion: Warm air over cooler air that traps pollution near the ground.
RAAN: The Valley Air District's Real-time Air Advisory Network of hourly readings.
MERV: Minimum Efficiency Reporting Value, a 1–16 rating of how well a filter captures particles.
HEPA: A portable air cleaner filter standard; HEPA doesn't belong in a residential HVAC system.
Filterbuy: A U.S. maker of pleated HVAC air filters based in Talladega, Alabama.