Air quality
Air quality in Union City today
Updated
Moderate (US AQI 55) Acceptable for most people. Unusually sensitive people should consider shortening long or heavy exertion outdoors. Model estimate for Sun, Oct 25, 5:00 pm (00:00 UTC).
Live AQI, PM2.5, PM10 and ozone for Union City, California, United States, with a 48-hour forecast and the best time to be outside.
- US AQI now
- 55 Moderate
- PM2.5
- 13 µg/m³ 0.9× WHO 24-h guideline
- PM10
- 14 µg/m³
- Ozone
- 75 µg/m³
- Dominant pollutant
- PM2.5 sub-index 55
- Best hour today
- 5:00 pm AQI 55
- European AQI
- 37
Air quality in Union City right now
Right now the modelled US Air Quality Index for Union City, California, United States is 55, which falls in the "Moderate" band (up to 100). Acceptable for most people. Unusually sensitive people should consider shortening long or heavy exertion outdoors.
The index is driven mainly by PM2.5, whose own sub-index is 55. 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 13 µg/m³, within the WHO 24-hour guideline of 15 µg/m³; PM10 is 14 µg/m³ against a guideline of 45; ozone is 75 µg/m³ (below the WHO 8-hour level of 100); nitrogen dioxide is 22 µg/m³ (below the 24-hour guideline of 25).
Also this hour: carbon monoxide 174 µg/m³.
NASA FIRMS shows 30 fire hotspots within 300 km in the last day (nearest about 17 km), but particle levels are not elevated enough to point to smoke right now.
Union City AQI forecast: next 48 hours
Over the next 24 hours the AQI is forecast to range from 55 around Sun 5:00 pm to 73 around Mon 12:00 pm, staying "Moderate" throughout.
The following day is expected to be cleaner, averaging about 58 against 65 for the next 24 hours.
| Local time (America/Los_Angeles) | US AQI | Category | PM2.5 µg/m³ | PM10 µg/m³ | Ozone µg/m³ |
|---|---|---|---|---|---|
| Sun 5:00 pm | 55 | Moderate | 13.4 | 14 | 75 |
| Sun 8:00 pm | 58 | Moderate | 24.7 | 26 | 9 |
| Sun 11:00 pm | 60 | Moderate | 28.3 | 30 | 6 |
| Mon 2:00 am | 62 | Moderate | 30.9 | 33 | 7 |
| Mon 5:00 am | 65 | Moderate | 30.7 | 33 | 13 |
| Mon 8:00 am | 69 | Moderate | 24.8 | 29 | 13 |
| Mon 11:00 am | 72 | Moderate | 10.1 | 14 | 68 |
| Mon 2:00 pm | 73 | Moderate | 7.2 | 10 | 81 |
| Mon 5:00 pm | 73 | Moderate | 6.5 | 9 | 76 |
| Mon 8:00 pm | 70 | Moderate | 6.3 | 8 | 51 |
| Mon 11:00 pm | 66 | Moderate | 8.2 | 10 | 30 |
| Tue 2:00 am | 61 | Moderate | 8.8 | 11 | 30 |
| Tue 5:00 am | 55 | Moderate | 10 | 13 | 34 |
| Tue 8:00 am | 51 | Moderate | 13.3 | 16 | 24 |
| Tue 11:00 am | 48 | Good | 8.7 | 12 | 71 |
| Tue 2:00 pm | 48 | Good | 9 | 13 | 85 |
| Tue 5:00 pm | 50 | Good | 9.9 | 14 | 82 |
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 Union City today
Between 6 am and 9 pm local time, the cleanest air today is forecast around 5:00 pm (AQI 55, Moderate) and the worst around 8:00 pm (AQI 58). The difference across the day is small, so timing matters little.
Union City vs the rest of United States
Across 747 United States cities we track, the average US AQI right now is 52 (Moderate). Union City at 55 is about average.
It ranks 572 of 747 from cleanest to most polluted; the cleanest is Hilo (20) and the most polluted Springfield, PA (133).
For context, the median across 3,909 cities worldwide is 57.
Air quality in cities near Union City
| City | Distance | US AQI | Category | PM2.5 µg/m³ |
|---|---|---|---|---|
| Fremont | 6 km | 60 | Moderate | 17.2 |
| Newark, CA | 8 km | 60 | Moderate | 17.2 |
| Hayward | 10 km | 60 | Moderate | 17.2 |
| Ashland | 14 km | 60 | Moderate | 17.2 |
| Dublin, CA | 14 km | 60 | Moderate | 17.2 |
| Belmont | 24 km | 61 | Moderate | 14.4 |
| Sunnyvale | 25 km | 54 | Moderate | 8.5 |
| San Mateo, CA | 27 km | 61 | Moderate | 14.4 |
Model vs measured
The nearest measured PM2.5 reading is 3.7 µg/m³ from Sensor.Community (median of 3 sensors), centred about 21 km from the city centre. That is 9.7 µg/m³ below the model estimate of 13 µg/m³. Low-cost sensors can read high in humid air; reference monitors are more accurate but sparser.
Advice for sensitive groups
At 55, most people are fine outdoors. If you are unusually sensitive to PM2.5, keep long or intense workouts to the cleaner hours shown above.
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 Union City
Air quality elsewhere
Data: Open-Meteo Air Quality API, Copernicus Atmosphere Monitoring Service (CAMS), Sensor.Community, NASA FIRMS.