Air quality
Air quality in Longmont today
Updated
Good (US AQI 48) Air quality is satisfactory and poses little or no risk; a good time for outdoor activity. Model estimate for Sun, Oct 25, 8:00 pm (02:00 UTC).
Live AQI, PM2.5, PM10 and ozone for Longmont, Colorado, United States, with a 48-hour forecast and the best time to be outside.
- US AQI now
- 48 Good
- PM2.5
- 12 µg/m³ 0.8× WHO 24-h guideline
- PM10
- 12 µg/m³
- Ozone
- 40 µg/m³
- Dominant pollutant
- PM2.5 sub-index 48
- Best hour tomorrow
- 9:00 pm AQI 25
- European AQI
- 34
Air quality in Longmont right now
Right now the modelled US Air Quality Index for Longmont, Colorado, United States is 48, which falls in the "Good" band (up to 50). Air quality is satisfactory and poses little or no risk; a good time for outdoor activity.
The index is driven mainly by PM2.5, whose own sub-index is 48. Fine and coarse particles come from traffic, heating, industry, dust and smoke; they build up on calm nights and clear when wind or rain arrives.
PM2.5 is 12 µg/m³, within the WHO 24-hour guideline of 15 µg/m³; PM10 is 12 µg/m³ against a guideline of 45; ozone is 40 µg/m³ (below the WHO 8-hour level of 100); nitrogen dioxide is 17 µg/m³ (below the 24-hour guideline of 25).
Also this hour: carbon monoxide 145 µg/m³.
Longmont AQI forecast: next 48 hours
Over the next 24 hours the AQI is forecast to range from 26 around Mon 6:00 pm to 49 around Sun 10:00 pm, staying "Good" throughout.
The following day is expected to be cleaner, averaging about 26 against 38 for the next 24 hours.
| Local time (America/Denver) | US AQI | Category | PM2.5 µg/m³ | PM10 µg/m³ | Ozone µg/m³ |
|---|---|---|---|---|---|
| Sun 8:00 pm | 48 | Good | 11.8 | 12 | 40 |
| Sun 11:00 pm | 48 | Good | 7 | 7 | 31 |
| Mon 2:00 am | 45 | Good | 7.6 | 8 | 36 |
| Mon 5:00 am | 42 | Good | 1.9 | 2 | 40 |
| Mon 8:00 am | 37 | Good | 0.9 | 1 | 36 |
| Mon 11:00 am | 33 | Good | 1.2 | 1 | 45 |
| Mon 2:00 pm | 31 | Good | 1.5 | 2 | 61 |
| Mon 5:00 pm | 27 | Good | 2.2 | 2 | 59 |
| Mon 8:00 pm | 26 | Good | 6.7 | 7 | 36 |
| Mon 11:00 pm | 22 | Good | 9.1 | 9 | 23 |
| Tue 2:00 am | 21 | Good | 4.4 | 5 | 40 |
| Tue 5:00 am | 19 | Good | 3.2 | 3 | 53 |
| Tue 8:00 am | 21 | Good | 5.2 | 5 | 49 |
| Tue 11:00 am | 24 | Good | 3.5 | 4 | 75 |
| Tue 2:00 pm | 30 | Good | 2.9 | 4 | 94 |
| Tue 5:00 pm | 37 | Good | 2.6 | 3 | 79 |
| Tue 8:00 pm | 38 | Good | 8.3 | 9 | 39 |
Every third hour of the CAMS forecast via Open-Meteo. US AQI uses rolling averages (24 h for particles, 8 h for ozone), so it moves more slowly than the hourly concentrations.
Best time to be outside in Longmont tomorrow
Between 6 am and 9 pm local time, the cleanest air tomorrow is forecast around 9:00 pm (AQI 25, Good) and the worst around 6:00 am (AQI 40). That is a swing of 15 points, so a run or walk around 9:00 pm is noticeably better.
Longmont vs the rest of United States
Across 619 United States cities we track, the average US AQI right now is 52 (Moderate). Longmont at 48 is about average.
It ranks 198 of 619 from cleanest to most polluted; the cleanest is Hilo (22) and the most polluted Springfield, PA (132).
For context, the median across 3,556 cities worldwide is 58.
Air quality in cities near Longmont
| City | Distance | US AQI | Category | PM2.5 µg/m³ |
|---|---|---|---|---|
| Erie, CO | 14 km | 44 | Good | 7.2 |
| Louisville, CO | 21 km | 44 | Good | 7.2 |
| Boulder | 22 km | 44 | Good | 7.2 |
| Brighton, CO | 31 km | 47 | Good | 5.6 |
| Thornton | 35 km | 44 | Good | 6.4 |
| Westminster | 37 km | 44 | Good | 6.4 |
| Windsor, CO | 38 km | 39 | Good | 9 |
| Arvada | 41 km | 44 | Good | 6.4 |
Model vs measured
We found no measured PM2.5 sensor cell within 25 km of Longmont, so the numbers on this page are model estimates. Models capture regional pollution well but can miss very local sources such as a busy road or a nearby fire.
Advice for sensitive groups
With the AQI at 48, there is no need for sensitive groups to change plans. People with asthma should still carry their reliever inhaler as usual.
What the US AQI numbers mean
| US AQI | Category | What it means |
|---|---|---|
| 0-50 | Good | Air quality is satisfactory and poses little or no risk; a good time for outdoor activity. |
| 51-100 | Moderate | Acceptable for most people. Unusually sensitive people should consider shortening long or heavy exertion outdoors. |
| 101-150 | Unhealthy for Sensitive Groups | People with heart or lung disease, older adults, children and teens should cut back on prolonged or heavy exertion outdoors. |
| 151-200 | Unhealthy | Everyone should reduce prolonged or heavy exertion outdoors; sensitive groups should avoid it and keep windows closed. |
| 201-300 | Very Unhealthy | Health alert: everyone should avoid prolonged or heavy exertion outdoors, and sensitive groups should stay indoors. |
| 301-500 | Hazardous | Emergency conditions: everyone should avoid all outdoor physical activity and stay indoors with filtered air if possible. The scale tops out at 500; heavier dust or smoke is shown as 500. |
Values on this page are modelled by CAMS (Copernicus) and served by Open-Meteo; they are estimates for the area around the city centre, not readings from an official monitor.
Nearby cities
More for Longmont
Air quality elsewhere
Data: Open-Meteo Air Quality API, Copernicus Atmosphere Monitoring Service (CAMS).