We’ve watched Denver’s AQI move from 38 to 150 in a single afternoon. No smoke on the horizon. No advisory issued yet. Just ground-level ozone building through the heat of the day the way it does on every Front Range summer afternoon above 80°F.
That reading matters inside your home as much as it does outside. This page covers Colorado’s current AQI map, explains what each reading means for your health, and tells you what to do about the air in your house when outdoor conditions deteriorate. Data comes from the EPA’s AirNow monitoring network and CDPHE, which publishes real-time readings from continuous monitoring stations across the state every hour.
Two pollutants drive nearly every Colorado AQI spike. Ground-level ozone peaks on hot summer afternoons across the Front Range. PM2.5 — fine particulate matter — spikes during wildfire season, typically June through October. Knowing which one is active today changes how you protect your household.
TL;DR Quick Answers
What Is the Live Air Quality Index (AQI) Map for Colorado Now and Today?
Colorado’s live AQI updates hourly from CDPHE monitoring stations statewide. Current readings vary by region:
- Front Range (Denver, Boulder, Fort Collins): Most vulnerable to ozone spikes in summer and PM2.5 from wildfire smoke August–October
- Mountain communities: Typically cleaner baseline; watch for winter temperature inversions in valley towns
- Eastern Plains: Generally lower readings year-round except during statewide smoke events
Where to check Colorado’s live AQI right now: Colorado Live AQI Map — Filterbuy | EPA AirNow Colorado | CDPHE Official Portal
What the number means for your home: AQI above 100 — run MERV 11. AQI above 150 — upgrade to MERV 13 if your system supports it. Closing windows helps; the filter determines how much.
Top Takeaways
- Colorado’s AQI is driven by two primary pollutants: ground-level ozone on hot Front Range afternoons (peak season: June–August) and PM2.5 from wildfire smoke (peak season: June–October). Knowing which one is active today changes your protective response.
- Denver has ranked 6th worst nationally for ozone pollution three consecutive years — a structural problem tied to the city’s geography and elevation, not a bad-luck streak.
- CDPHE publishes real-time AQI readings every hour from continuous monitoring stations statewide. AirNow.gov and the CDPHE portal are the two authoritative sources for live and forecast conditions.
- MERV 8 is undersized for Colorado wildfire smoke events. MERV 11 is the recommended year-round baseline for Front Range households. MERV 13 provides the strongest protection during AQI events above 150 — verify system compatibility before upgrading.
- Running your AC in recirculation mode during high-AQI days reduces outdoor air infiltration. Pair this with the right MERV filter to cut indoor PM2.5 exposure during smoke events.
Table of Contents
What Is the Air Quality Index (AQI) — and How Is It Measured?
The Air Quality Index is a federal 0-to-500 scale the EPA developed to translate raw pollutant data into one readable number. Higher numbers mean more pollution and greater health risk. The full technical breakdown lives in the Air Quality Index (AQI, but here’s what actually matters for Colorado residents.
The AQI tracks six pollutants: ground-level ozone, PM2.5, PM10, carbon monoxide, sulfur dioxide, and nitrogen dioxide. In Colorado, ozone and PM2.5 account for the overwhelming majority of high-AQI days. The other four are worth knowing. These two are what you’re actually dealing with most of the time.
Here’s how to read the AQI scale:
The AQI runs from 0 to 500. Readings between 0 and 50 are Good — no restrictions, any outdoor activity is fine. From 51 to 100, air quality is Moderate and acceptable for most people, though unusually sensitive individuals may start to notice symptoms. Once the reading hits 101 to 150, the category shifts to Unhealthy for Sensitive Groups: children, the elderly, and anyone with asthma or heart conditions should reduce outdoor exertion. At 151 to 200 — Unhealthy — everyone can experience health effects, and prolonged outdoor activity should be avoided. From 201 to 300, the air is Very Unhealthy; this is a health alert level where everyone should stay indoors, and your HVAC should be running with a MERV 13 filter. Anything above 300 is hazardous — emergency conditions where staying indoors is non-negotiable and maximum indoor filtration is the only meaningful protective step you can take.
Colorado Air Quality Today — What Drives AQI Across the State
Colorado doesn’t have a single AQI reading. It has a patchwork of conditions shaped by geography, elevation, and season. The reading near you today may reflect a local event, a statewide smoke pattern, or both.
The Front Range: Ground-Level Ozone
Denver, Boulder, Fort Collins, and Colorado Springs sit at the base of the Rockies in a natural bowl that traps air. On days above 80°F with clear skies, sunlight reacts with vehicle emissions and industrial pollutants to produce ground-level ozone. Colorado’s elevation makes this worse. More UV radiation reaches the surface here than at lower-altitude cities, which accelerates the chemical reaction.
Ozone season on the Front Range runs April through September, peaking in June, July, and August. CDPHE issues Ozone Action Days when forecasts indicate exceedances. On those days, commuters are asked to reduce driving and residents to avoid lawn mowing or refueling before 5 PM.
Statewide: Wildfire Smoke and PM2.5
From June through October, wildfire smoke is Colorado’s dominant AQI variable. PM2.5 from in-state fires and transported smoke from Utah, New Mexico, and California can push readings from Good to Unhealthy in hours. Western Slope communities typically see elevated readings first. The smoke then moves east across the Continental Divide toward Front Range population centers.
PM2.5 events don’t follow the same daily arc as ozone. Ozone builds through the day and falls after sunset. Wildfire smoke arrives overnight, persists for days, and can hit multiple regions at once. When you see haze on the horizon and the sky turns orange or brown, check the PM2.5 reading specifically, not just the composite AQI number.
Mountain Communities and Eastern Plains
Mountain towns like Steamboat Springs, Telluride, and Glenwood Springs run cleaner baseline readings than the Front Range. Mountain valleys are a different story in winter: cold air traps pollutants near the valley floor during temperature inversions, sometimes for days. The Roaring Fork Valley and Eagle County are the most documented Colorado examples.
The Eastern Plains maintain lower AQI readings year-round. The consistent exception is transported wildfire smoke events that affect the entire state simultaneously.
Where to Monitor Colorado AQI in Real Time
Accurate real-time AQI data for Colorado requires sources pulling directly from the CDPHE monitoring network, not weather apps that estimate air quality from satellite data alone.
Sources we reference and recommend:
- EPA AirNow — Colorado State Page: The federal standard for real-time AQI data, pulling from CDPHE’s continuous monitoring network. Updated hourly.
- CDPHE Air Quality Portal (colorado.gov/airquality): Colorado’s official statewide monitoring dashboard, including AQI forecasts, Ozone Action Days, and Front Range advisories.
- The Colorado live AQI map on Filterbuy provides a real-time statewide view by monitoring stations.
- EPA Fire and Smoke Map (fire.airnow.gov): The most useful tool during active wildfire events. Shows PM2.5 concentration overlays from current fire activity across the Western US.
- AirNow Mobile App: Available for iOS and Android. Send push notifications when AQI crosses thresholds at your location.
AQI readings vary significantly between stations in Colorado. A reading of AQI 75 in Denver tells you nothing about conditions in Boulder or Pueblo. During wind-driven smoke events especially, check the station closest to your location.
Denver Air Quality Index Today — A City-Level Look
Denver consistently ranks among the most challenging major US cities for air quality. The Denver-Aurora-Greeley metro has ranked 6th worst nationally for ozone pollution three consecutive years, per the American Lung Association’s State of the Air reports. That context matters when you’re reading today’s AQI for Denver.
The city’s elevation — 5,280 feet — is both an asset and an air quality liability. Thinner atmosphere means more UV radiation at the surface, which accelerates ozone formation on sunny, warm days. The I-25 and I-70 corridors supply the nitrogen oxides and volatile organic compounds that fuel that reaction.
Denver’s worst AQI periods, by season:
- July–August: Ozone peaks. Hot temperatures, clear skies, and stagnant air regularly push AQI above 100. CDPHE issues Ozone Action Day advisories throughout this window.
- August–October: Wildfire smoke season. PM2.5 from regional fires can drive AQI higher even as ozone declines. The two events sometimes overlap in September, creating compound high-AQI days.
- December–February: Winter temperature inversions. Cold, stagnant air settles over the Denver Basin, trapping emissions near the surface. Less severe than summer peaks, but these events can persist for multiple days.
For Denver specifically: if today’s AQI is above 100 on a summer afternoon, ozone is almost certainly the driver. If it spikes overnight or early morning and haze is visible, PM2.5 from smoke is more likely. CDPHE’s advisory page identifies which pollutant is responsible for each Action Day.
How Colorado’s AQI Affects Your Home’s Indoor Air Quality
Most people check the AQI and adjust their outdoor plans. Fewer make the connection to what’s happening inside their home, through the HVAC system specifically. We work with this connection every day. It’s why air quality monitoring isn’t just an outdoor habit.
Here’s how we match HVAC filter selection to Colorado’s AQI conditions:
When Colorado’s AQI sits between 0 and 50, a MERV 8 or higher filter handles the load on a normal replacement schedule — no changes needed. From 51 to 100, most households can hold steady, though sensitive individuals should consider stepping up to MERV 11. Once readings climb into the 101 to 150 range, MERV 11 becomes the standard: upgrade if you haven’t already, keep windows closed, and run your HVAC on a tighter schedule. At 151 to 200, MERV 13 is the minimum — shorten your replacement interval and switch your AC to recirculation mode to cut outdoor air draw. Above 200, the protocol shifts to maximum protection: MERV 13 filter, recirculation mode, and a portable HEPA purifier running in occupied rooms. Before installing MERV 13 at any AQI level, verify your system’s static pressure rating — a filter your system can’t handle reduces total filtered air volume and defeats the purpose entirely.
MERV 13 captures PM2.5 far better than MERV 8 or MERV 11 — but it also raises static pressure on your air handler. Before upgrading, check your system’s rated capacity. A filter the system can’t handle creates its own problem: reduced airflow and faster blower wear. A MERV 11 running on a properly rated system beats a MERV 13 fighting restricted airflow every time.
“On the worst wildfire smoke days we’ve tracked across Colorado-adjacent HVAC evaluations, homes running MERV 8 filters measured indoor PM2.5 levels high enough to trigger symptoms in healthy adults — not just the sensitive groups most air quality warnings focus on. Closing the windows buys you something; the filter is what determines how much.”
— FilterKnowHow.com HVAC & IAQ Field Team
Essential Resources for Monitoring Colorado Air Quality
These are the monitoring tools and source documents our team uses and recommends for tracking Colorado’s live AQI, understanding current pollutant conditions, and protecting indoor air quality when outdoor readings climb.
1. EPA AirNow — Colorado State Page
The federal government’s official real-time air quality monitoring interface. AirNow pulls directly from CDPHE’s statewide continuous monitoring network and updates AQI readings hourly. It includes city-level forecasts, interactive maps, and email or text alerts tied to your zip code.
URL: https://www.airnow.gov/state/?name=colorado
2. CDPHE Air Quality Portal — Official Colorado State Dashboard
The Colorado Department of Public Health and Environment’s Air Pollution Control Division publishes real-time AQI data, daily AQI forecasts, Ozone Action Day advisories, and the Front Range air quality advisory for the seven-county Denver-Boulder metro area. This is the authoritative source for Colorado-specific conditions.
URL: https://www.colorado.gov/airquality/
3. EPA Fire and Smoke Map
During wildfire events, this map is the most useful tool available. It overlays PM2.5 concentration data from active fires, smoke forecasts, and real-time satellite imagery across the Western US. Developed jointly by the EPA and the US Forest Service, it shows clearly when and where wildfire smoke is likely to affect Colorado’s AQI.
4. Filterbuy Colorado Live AQI Map
Provides a real-time statewide view of Colorado AQI conditions across major monitoring stations. Useful for quickly checking conditions before outdoor activity or cross-referencing regional readings during smoke events.
5. Wikipedia: Air Quality Index
The go-to public reference for understanding how the AQI scale was developed, how individual pollutant sub-indices are calculated, and how the US AQI system compares internationally. Worth reading if you want the technical foundation behind the numbers.
URL: https://en.wikipedia.org/wiki/Air_quality_index
6. CDPHE Ozone Pollution and Your Health
Colorado-specific guidance from CDPHE on ground-level ozone: how it forms at altitude, which populations face the highest risk, and how to cut exposure during Ozone Action Days. Includes the division’s public-facing Ozone Action Day tracker and Front Range forecast archive.
URL: https://cdphe.colorado.gov/ozone-pollution-and-your-health
7. CDPHE Air Monitoring Data and Technical Reports
For verified historical AQI data, annual monitoring reports, and network documentation, CDPHE’s technical report archive covers Colorado’s full air monitoring dataset. Includes ozone exceedance tallies, PM2.5 annual averages, and network plans by county.
URL: https://cdphe.colorado.gov/public-information/air-monitoring-data-and-technical-reports
Three Data Points That Put Today’s Colorado AQI in Context
Stat 1 — Denver’s National Ozone Ranking
The Denver-Aurora-Greeley metro ranked 6th worst in the nation for ozone pollution for the third consecutive year, per the American Lung Association’s 2025 State of the Air report, which analyzed EPA-verified air quality data from 2021–2023.
Denver’s ozone problem isn’t a bad-year outlier. It’s a structural, recurring issue tied to the city’s geography, population growth, and elevation. Checking the live ozone AQI before outdoor exercise in summer isn’t optional for sensitive populations in this metro — it’s a basic precaution.
Source: American Lung Association — 2025 State of the Air Report | lung.org/media/press-releases/co-sota-2025-denver-release
Stat 2 — How Often Denver Air Crosses the ‘Good’ Threshold
EPA monitoring records show metro Denver residents experienced at least 265 days of above-Good AQI in 2019, including 243 moderate days and 22 days in the Unhealthy for Sensitive Groups category or worse. In 2018 — a severe wildfire year — that figure rose to 282 days.
Denver is not a city where you replace your HVAC filter every 90 days and call it sufficient. With air quality above the Good threshold for roughly 70–75% of the year in average-to-bad wildfire seasons, filter loading happens faster here than in most US metros.
Source: Denver Post / EPA Records | denverpost.com/2020/01/30/denver-air-pollution-worst-cities/
Stat 3 — EPA Reclassified Denver as ‘Serious’ Nonattainment for Ozone
Since 2019, the EPA has designated nine Colorado Front Range counties — including the Denver metro — as Serious Nonattainment areas for ozone, a classification for regions that have failed to meet federal ozone health standards for a decade or more.
Serious Nonattainment isn’t a designation that stays in a government database. It means federal ozone standards are being exceeded at a level requiring mandatory state action plans and additional monitoring. It’s the regulatory confirmation that the Front Range’s ozone problem is chronic — and that checking the live AQI before outdoor activity on summer afternoons is a real health precaution.
Source: CDPHE / EPA Nonattainment Designation | cdphe.colorado.gov/ozone-pollution-and-your-health
Our Take: Colorado’s Air Quality Problem Is Underestimated Indoors
The clean-air reputation Colorado carries is real for mountain towns on a clear January morning. On the Front Range in August, during a smoke event, it doesn’t describe the air people are actually breathing.
Serious Ozone Nonattainment. Sixth-worst nationally for ozone three years running. Wildfire seasons now run June through October. These aren’t anomalies. They’re the conditions Colorado homeowners are navigating every year — and they change what HVAC filtration actually requires.
What concerns us most from a field perspective is the indoor protection gap. Homeowners check the AQI, see a reading they’re not sure how to interpret, close their windows, and assume the home is now protected. Closing the windows helps. But a MERV 8 filter — the default in most systems — offers meaningful protection against dust and pollen and almost nothing against the PM2.5 particles wildfire smoke carries.
Our position, based on what we’ve observed and evaluated: if you live on the Colorado Front Range, your baseline filter should be MERV 11 year-round. During documented smoke events or AQI readings above 150, upgrade to MERV 13 if your system supports it. This isn’t theoretical. It’s the practical response to what the data shows about how often Colorado’s air quality creates conditions a MERV 8 filter was never built for.
The live AQI map tells you what’s happening outside. Your filter determines what that means inside. They’re not separate decisions.
Frequently Asked Questions
Q: What is the current AQI in Colorado today?
Colorado’s AQI varies by region and updates hourly. For live, station-specific readings, check the EPA AirNow Colorado page at airnow.gov or the CDPHE statewide portal at colorado.gov/airquality. The Filterbuy Colorado live AQI map also provides a statewide view updated in real time.
Q: What is a good AQI level in Colorado?
AQI 0–50 (Good, Green) is the target. Most outdoor activities are safe below 100. Above 100, sensitive groups — children, elderly, and those with asthma or heart conditions — should start limiting extended outdoor exertion. Above 150, everyone should act.
Q: Is Colorado air quality bad today?
It depends on location and season. The Front Range — Denver, Boulder, Fort Collins — faces the most frequent air quality challenges from ozone and wildfire smoke. Mountain communities typically run cleaner. Eastern Plains readings are generally lower except during statewide smoke events. Always check your nearest monitoring station.
Q: How does wildfire smoke affect Colorado AQI?
Wildfire smoke is a PM2.5 event — it spikes fine particulate readings, not ozone. It can push Colorado AQI from Good to Unhealthy within hours and persist for multiple days. PM2.5 from smoke doesn’t stop at closed windows. It infiltrates through building gaps and HVAC intakes, which makes filter selection critical during fire season.
Q: What MERV filter rating do I need during Colorado wildfire smoke?
MERV 13 is recommended when wildfire smoke pushes AQI above 150. MERV 11 provides meaningful protection during moderate smoke conditions (AQI 101–150). MERV 8 — the standard default in many systems — isn’t rated to capture the fine PM2.5 particles wildfire smoke carries. Check your system’s static pressure rating before installing MERV 13.
Q: What is Denver’s air quality index today?
Denver’s live AQI is available at AirNow.gov (search ‘Denver, CO’) and at the CDPHE portal. Denver’s worst AQI months are July–August for ozone and August–October for wildfire smoke. The two can overlap in September, creating compound high-AQI days. Check the live reading, not a seasonal average, for today’s conditions.
Q: How often does Colorado have Unhealthy AQI days?
On the Front Range, EPA records show Denver has exceeded the Good AQI threshold for anywhere from 200 to 280-plus days in recent years, with the higher figures occurring in severe wildfire years like 2018. Days crossing into the Unhealthy range (AQI 150+) are less frequent but have increased alongside longer, more intense wildfire seasons. CDPHE publishes annual AQI summary data for all monitoring regions.
Colorado’s Live AQI Map Is One Tab Away — So Is Knowing Whether Your Filter Is Ready for It
Check today’s conditions on the Colorado Live AQI Map, then match your MERV rating to what you find — because the number outside determines what the air inside your home actually is.