Air quality
Air quality in Castle Rock today
Updated
Good (US AQI 33) Air quality is satisfactory and poses little or no risk; a good time for outdoor activity. Model estimate for Sun, Oct 25, 6:00 pm (00:00 UTC).
Live AQI, PM2.5, PM10 and ozone for Castle Rock, Colorado, United States, with a 48-hour forecast and the best time to be outside.
- US AQI now
- 33 Good
- PM2.5
- 1.8 µg/m³ 0.1× WHO 24-h guideline
- PM10
- 2.6 µg/m³
- Ozone
- 69 µg/m³
- Dominant pollutant
- ozone sub-index 33
- Best hour today
- 6:00 pm AQI 33
- European AQI
- 25
Air quality in Castle Rock right now
Right now the modelled US Air Quality Index for Castle Rock, Colorado, United States is 33, 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 ozone, whose own sub-index is 33. Ozone usually peaks in the afternoon on sunny days and falls back after sunset.
PM2.5 is 1.8 µg/m³, within the WHO 24-hour guideline of 15 µg/m³; PM10 is 2.6 µg/m³ against a guideline of 45; ozone is 69 µg/m³ (below the WHO 8-hour level of 100); nitrogen dioxide is 3.6 µg/m³ (below the 24-hour guideline of 25).
Also this hour: carbon monoxide 155 µg/m³.
NASA FIRMS shows 2 fire hotspots within 300 km in the last day (nearest about 290 km), but particle levels are not elevated enough to point to smoke right now.
Castle Rock AQI forecast: next 48 hours
Over the next 24 hours the AQI is forecast to range from 18 around Mon 10:00 am to 35 around Mon 6:00 pm, staying "Good" throughout.
The following day is expected to be worse, averaging about 32 against 25 for the next 24 hours.
| Local time (America/Denver) | US AQI | Category | PM2.5 µg/m³ | PM10 µg/m³ | Ozone µg/m³ |
|---|---|---|---|---|---|
| Sun 6:00 pm | 33 | Good | 1.8 | 3 | 69 |
| Sun 9:00 pm | 33 | Good | 3.5 | 5 | 42 |
| Mon 12:00 am | 27 | Good | 8.1 | 9 | 47 |
| Mon 3:00 am | 22 | Good | 4.5 | 5 | 42 |
| Mon 6:00 am | 20 | Good | 0.9 | 1 | 40 |
| Mon 9:00 am | 19 | Good | 1.9 | 2 | 36 |
| Mon 12:00 pm | 19 | Good | 0.9 | 1 | 72 |
| Mon 3:00 pm | 26 | Good | 1 | 1 | 91 |
| Mon 6:00 pm | 35 | Good | 1.8 | 2 | 78 |
| Mon 9:00 pm | 37 | Good | 4.2 | 5 | 57 |
| Tue 12:00 am | 32 | Good | 3.3 | 4 | 58 |
| Tue 3:00 am | 28 | Good | 2.6 | 4 | 57 |
| Tue 6:00 am | 26 | Good | 2.4 | 3 | 53 |
| Tue 9:00 am | 25 | Good | 3.1 | 4 | 56 |
| Tue 12:00 pm | 28 | Good | 1.4 | 2 | 106 |
| Tue 3:00 pm | 38 | Good | 1.2 | 2 | 106 |
| Tue 6:00 pm | 45 | Good | 2.4 | 3 | 80 |
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 Castle Rock today
Between 6 am and 9 pm local time, the cleanest air today is forecast around 6:00 pm (AQI 33, Good) and the worst around 7:00 pm (AQI 34). The difference across the day is small, so timing matters little.
Castle Rock vs the rest of United States
Across 747 United States cities we track, the average US AQI right now is 52 (Moderate). Castle Rock at 33 is 19 points cleaner than average.
For context, the median across 3,909 cities worldwide is 57.
Air quality in cities near Castle Rock
| City | Distance | US AQI | Category | PM2.5 µg/m³ |
|---|---|---|---|---|
| Centennial | 23 km | 45 | Good | 3.2 |
| Aurora | 40 km | 45 | Good | 3.2 |
| Lakewood | 42 km | 45 | Good | 3.2 |
| Denver | 42 km | 45 | Good | 3.2 |
| Arvada | 52 km | 45 | Good | 3.2 |
| Golden | 53 km | 42 | Good | 4.9 |
| Westminster | 54 km | 45 | Good | 3.2 |
| Thornton | 56 km | 45 | Good | 3.2 |
Model vs measured
We found no measured PM2.5 sensor cell within 25 km of Castle Rock, 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 33, 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 Castle Rock
Air quality elsewhere
Data: Open-Meteo Air Quality API, Copernicus Atmosphere Monitoring Service (CAMS), NASA FIRMS.