Worst air pollution Longmont, today and tomorrow
Today (20 September): Air quality in Longmont is moderate. AQI, NO2, and O3 are moderate; PM2.5 is fair; PM10, SO2, CO, HCHO, and PM1 are good. Pollution peaks around 10:00 AM (O3: 41.5/100).
Tomorrow (21 September 2026): Air quality in Longmont is poor. AQI worsens to poor; O3 increases to poor; all other pollutants stay as today. Pollution peaks around 9:00 AM (O3: 60.4/100). Airmine updates local air quality forecasts four times daily.
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Developed with support from the European Space Agency (ESA)’s Business Applications and Space Solutions (BASS) team
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Longmont's air quality reflects the Front Range position north of Denver, with vehicle emissions from US-287 and the surrounding technology and oil and gas extraction operations in the Denver-Julesburg Basin contributing local sources. The Rocky Mountains provide clean westerly airflows on most days, while the Front Range temperature inversion problem periodically affects the northern Boulder County corridor and summer wildfire smoke from Colorado forests is an increasingly frequent seasonal concern.
Today - 20 September | Pollution peaks at 10:00
AQI:
Moderate
41.5/100
PM2.5 (fine particles):
Fair
33.0/100
PM10 (coarse particles):
Good
17.6/100
NO2 (nitrogen dioxide):
Moderate
40.0/100
O3 (ozone):
Moderate
41.5/100
SO2 (sulfur dioxide):
Good
1.1/100
CO (carbon monoxide):
Good
0.6/100
HCHO (formaldehyde):
Good
2.7/100
PM1 (ultrafine particles):
Good
7.6/100
Levels show the poorest local air quality during the day
Tomorrow - 21 September | Pollution peaks at 09:00
AQI:
Poor
60.4/100
PM2.5 (fine particles):
Fair
21.8/100
PM10 (coarse particles):
Good
13.3/100
NO2 (nitrogen dioxide):
Moderate
45.4/100
O3 (ozone):
Poor
60.4/100
SO2 (sulfur dioxide):
Good
2.1/100
CO (carbon monoxide):
Good
0.6/100
HCHO (formaldehyde):
Good
3.8/100
PM1 (ultrafine particles):
Good
3.9/100
Pollen forecast in Longmont
View pollen forecastAir quality forecasts for neighbourhoods and landmarks in Longmont
Frequently Asked Questions
Is air quality bad in Longmont right now?
On 20 September 2026, overall air quality in Longmont is moderate. AQI is the main air quality indicator at 41.5/100. Pollution peaks around 10:00 AM (O3: 41.5/100).
Will air quality be worse tomorrow in Longmont?
On 21 September 2026, air quality conditions in Longmont will be worse than today, with AQI forecast at poor at 60.4/100. Pollution peaks around 9:00 AM (O3: 60.4/100).
When is air pollution at its worst in Longmont?
Longmont sees air quality change through the year, as a brief window in autumn tends to bring the year's best air, before winter inversions set in; by contrast, valley and basin locations can see pollution trapped under cold air for days during winter inversions. Higher-elevation, more exposed locations generally avoid the worst of the valley inversion episodes.
Are air quality levels in Longmont based on measurements or forecasts?
It is forecasts derived by downscaling forecasts provided by EU’s Copernicus Atmosphere Monitoring Service (CAMS) by taking into account local conditions such as traffic patterns. CAMS bases its forecast on satellite measurements of particles and chemical compounds in the atmosphere. Airmine’s services were developed with support from the European Space Agency (ESA)’s Business Applications and Space Solutions (BASS) team.
Why doesn’t the forecast always reflect wildfire impacts?
Airmine’s forecast uses CAMS (Copernicus Atmosphere Monitoring Service) as its background atmospheric model. While CAMS includes wildfire emissions, these are derived from satellite observations and are not available in real time. During rapidly evolving wildfire events, there may therefore be a delay before increased emissions are incorporated into the model. As a result, the forecast may temporarily underestimate PM₂.₅ and other pollutants associated with wildfire smoke.
During rapidly evolving wildfire events, CAMS may lag by approximately 1–2 days before increased wildfire emissions are fully represented, which can lead to temporary underestimation of PM₂.₅ concentrations in Airmine’s forecast.
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Data provided by Airmine — Last update: 20 September 2026 at 14:33 CEST (Data is updated four times daily.)
This forecast is produced independently using Airmine's own atmospheric data and models.
Unless explicitly made clear, the content on this site has not been paid for by external organisations and is Airmine's sole responsibility.
Disclaimer: Forecasts are provided for informational purposes only and should not be relied upon as medical advice. Actual pollen and air quality conditions may vary from the forecast. If you have allergies, asthma, or another medical condition, consult a healthcare professional. Please see our Terms of Service for important information about limitations of liability.
Some text on this page may be generated or summarised using artificial intelligence (AI). Wherever possible, AI-generated content is enriched with Airmine's proprietary data to improve its accuracy and relevance. However, AI-generated content may still contain errors, omissions, or inaccuracies.
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