Where does the air quality data come from?

From the OpenAQ open-data archive, which collects hourly measurements from government and research monitoring stations around the world. Each original provider is credited by OpenAQ; data licences vary by provider. The archive is published with a delay of about two to four days, so the latest values are usually from a few days ago.

Is the outlook a forecast?

No. It is a statistical trend: recent levels relaxing toward their two-week average, with a weekday pattern when there is enough history. It knows nothing about weather, fires or traffic. The page shows how well the same method did on the station's own past days compared with simply repeating the last value. For decisions, use your official air quality forecast.

How is the AQI calculated?

With the U.S. EPA breakpoints, including the 2024 PM2.5 revision: the 24-hour mean for PM2.5 and PM10, the highest 8-hour mean for ozone and CO, and the highest 1-hour value for NO2 and SO2. The day's AQI is the highest of the pollutant sub-indices. The latest PM values use the EPA NowCast.

Does it cost anything?

No. The example cities and your own CSV work without an account. Loading any other station needs a free SkillSafe sign-in and uses no credits.

Air quality for any city, and where it is heading

Pick a place to see its AQI day by day, which pollutant drives it, the cleanest hours to be outside and a 3-day statistical outlook. Measurements from thousands of public monitoring stations via OpenAQ.

Pick a place

Free examples, no sign-in:

Major cities

Or load your own air quality CSV

Drop a CSV here or choose a file

Either one row per reading (time, parameter, value, units) or a time column plus columns named pm25, pm10, o3, no2, so2, co. Read in your browser, never uploaded.

Gas columns without a unit are in Name for this data

Latest reading

Next 3 days: statistical outlook

A statistical trend, not an official forecast. It extends this station's recent pattern and knows nothing about weather, fires or traffic. Check your local air quality agency before making plans that matter.

Daily AQI

Pollutant levels

Days by category

Time of day

Daily data

How the numbers are made

AQI: U.S. EPA breakpoints with the 2024 PM2.5 revision. PM2.5 and PM10 use the 24-hour mean, ozone and CO the highest 8-hour mean of the day, NO2 and SO2 the highest hourly value. Ozone above 125 ppb in one hour also checks the 1-hour ozone table. The day's AQI is the highest sub-index; that pollutant is shown as the main one.
Units: particles in µg/m³; gases converted to ppb (CO to ppm) at 25 °C. When several sensors at one station report the same pollutant in the same hour, they are averaged.
Complete days: a day needs at least 6 hourly values for a pollutant; days with fewer than 18 are marked partial.
Latest reading: the EPA NowCast for PM2.5 and PM10 (the last 12 hours, weighted toward the most recent), otherwise the last hourly value. Archive timestamps mark the end of each hour; the page shows the hour's start.
Outlook: in log space, each pollutant's daily value relaxes from its latest level toward its mean of the previous 14 days at a rate fitted from the station's own day-to-day persistence, plus a weekday pattern when 6 or more weeks are loaded. The 80% range comes from the same method's errors on earlier days, each predicted only from the days before it. The track record compares those errors with repeating the last day's value.
WHO guidelines: 2021 levels: PM2.5 15 µg/m³ and PM10 45 µg/m³ (24-hour), ozone 100 µg/m³ (8-hour peak), NO2 25 µg/m³, SO2 40 µg/m³ and CO 4 mg/m³ (24-hour).
Time of day: the mean for each local clock hour over the loaded days, and the 3-hour windows with the lowest and highest mean.
Implausible values: negative readings and readings above 1500 µg/m³ PM2.5, 3000 µg/m³ PM10, 600 ppb ozone, 2000 ppb NO2 or SO2 and 60 ppm CO are left out; the page says how many above-cap readings it dropped.
Low-cost sensors and reference monitors are mixed in the archive; low-cost PM readings can run high in humid air.

About the data

Measurements come from the OpenAQ open-data archive, which gathers hourly readings from government, research and community monitoring stations in more than 100 countries and credits each original provider. Licences vary by provider; most government data are public or open-licence. Data: OpenAQ (openaq.org) and its original providers.

The archive is published with a delay of about two to four days, so “latest” means the newest archived hour. For live conditions and official forecasts, use your national or local air quality service.

Loading a station other than the examples asks the archive through this app's server and needs a free SkillSafe sign-in. Nothing you load is stored. A CSV you choose is read in your browser and never leaves it.