About the data (simple explanation)
This site shows air quality measurements published via OpenAQ. OpenAQ aggregates readings from many monitoring networks (government, research, and community sources). A city can have multiple stations, and each station can report multiple pollutants.
What does “latest” mean?
Most pages use the latest available readings for each city. That means it is a snapshot — not a daily average, not a forecast, and not a medical assessment. Some stations update frequently, others less often. We show timestamps when available.
Why do some cities look “empty”?
Sometimes a city has too few measurements, they are outdated, or they are inconsistent across sources. In these cases we avoid presenting a strong verdict and focus on showing what is available.
Pollutants explained (plain language)
Here are the most common measurements you may see on city pages:
| Code | Name | What it is | Why it matters |
|---|---|---|---|
| pm25 | PM2.5 | Very small particles (≤ 2.5 µm) from smoke, traffic, industry, heating. | Often the strongest day-to-day driver of health risk in cities. |
| pm10 | PM10 | Larger particles (≤ 10 µm), including dust, road particles, construction. | Can spike during dust events, heavy traffic, construction, or dry weather. |
| o3 | Ozone | A gas formed in sunlight from other pollutants (not emitted directly at street level). | Often higher on sunny afternoons; can irritate airways. |
| no2 | Nitrogen dioxide | A traffic/combustion-related gas (vehicles, power generation, heating). | Often higher near busy roads; contributes to smog chemistry. |
| so2 | Sulfur dioxide | A gas linked to burning sulfur-containing fuels (some industry, shipping, power plants). | Can be important in industrial or coastal/shipping areas. |
| co | Carbon monoxide | A gas from incomplete combustion (vehicles, heaters, wildfires). | Can increase during traffic or wildfire smoke episodes. |
| pm1 | PM1 | Ultra-fine particles (≤ 1 µm). Not available everywhere. | Useful additional detail when present; not always part of standard reporting. |
Availability depends on local monitoring networks. Some cities may show only PM, others include gases too.
Units: what do µg/m³, ppb, and ppm mean?
- µg/m³ (micrograms per cubic meter) — common for particles (PM2.5, PM10). It is a mass concentration in air.
- ppb / ppm — common for gases (ozone, NO2, SO2, CO). It describes how many parts of the air contain the gas.
Different networks may report different units. We preserve units as provided by the source, and we label them clearly on pages.
Important: this is not medical advice
This site does not provide medical advice. For official recommendations and health guidance, please use trusted sources: