Insights
What 25,585 recordings in buildings and 6,947 journeys on public transport reveal about the air we share indoors. A first look at the open dataset, as of 4 November 2026.
The dataset
Volunteers measure places open to the public with their own CO2 monitors, using the free IndoorCO2Map app. Each recording is linked to a place on OpenStreetMap, which gives every place a fixed ID and a type such as café or doctor’s practice. The app reads the monitor once a minute for at least five minutes, and the recording then appears on the map and in the open dataset.
25,585
recordings in buildings
12,009
places
57
countries
6,947
journeys on 1,337 transit lines
Open data export of 4 November 2026, recordings since April 2024. Around 95% of the data so far was collected with Aranet4 monitors.
Read this first: the limits of the data
- A first, exploratory look. For many categories the number of recordings is still low and not representative, so the results should be interpreted with caution. Some breakdowns rest on only a few places or journeys, such as 95 pubs or 17 Eurostar journeys, and mainly show what becomes possible as the dataset grows.
- Volunteers choose where to measure. That can bias the results, probably less for supermarkets, chemists and doctors’ practices and more for restaurants.
- Mostly Germany and Austria. About 70% of all recordings come from these two countries, so results for all countries mainly reflect them.
- Snapshots, not safety ratings. A recording shows the air at one moment, in one part of a building. The same place can be very different at another time, during an event or in another room.
Places
All countries, but most data from Germany and Austria
About three in ten pubs and bars average above 1,400 ppm, not a single DIY store does
Each bar shows how the measured places of one type are spread across the three CO2 levels of the GO IAQS Score by GO AQS (Global Open Air Quality Standards): good up to 800 ppm, moderate from 801 to 1,400 ppm and unhealthy above 1,400 ppm. Each place counts once, with the average of its recordings.
- Good: up to 800 ppm
- Moderate: 801 to 1,400 ppm
- Unhealthy: above 1,400 ppm
13%
of doctors’ practices average above 1,400 ppm
Only 39% stay at or below 800 ppm. In hospitals, the share above 1,400 ppm is 4%.
Only 29%
of pubs stay at or below 800 ppm
Pubs do worst overall. Yet every type of place in the chart also has places with good air, which shows that good air is achievable everywhere.
The bad tail by place type
Typical visits differ little between place types, the worst ones a lot
Averages hide the bad outliers. Each box shows the middle half of the visits to one place type, with the median as a line; the whiskers run from the 10th to the 90th percentile. Every place counts the same, however often it was measured, as if you visited each place once. The medians only range from about 570 ppm in DIY stores to 1,040 ppm in pubs, but the 90th percentiles from 720 to 2,720 ppm.
- Middle half of visits
- Median
- 10th to 90th percentile
- Numbers: 90th percentile in ppm
- Moderate from 801 ppm
- Unhealthy above 1,400 ppm
Pubs and bars: one visit in ten is above 2,700 ppm in pubs and nearly 2,500 ppm in bars, one in twenty above 3,900 ppm in pubs and 3,500 ppm in bars.
Doctors’ practices: one visit in ten is above 1,500 ppm, one in twenty about 1,800 ppm or more.
Schools are probably biased: most school measurements are likely taken by teachers who control the windows and are more aware of air quality than the average teacher.
Supermarkets in Germany
What the data shows · Germany
More than a third of Lidl stores and over a quarter of Aldi Süd stores average above 1,400 ppm
The chains sell similar goods in similar shops and still end up far apart. Kaufland is the only chain where most stores stay at or below 800 ppm; at Lidl and Aldi Süd, fewer than one store in ten does.
- Good: up to 800 ppm
- Moderate: 801 to 1,400 ppm
- Unhealthy: above 1,400 ppm
Public transport
Public transport · All countries
Trains have the worst air in public transport, trams the best
- Good: up to 800 ppm
- Moderate: 801 to 1,400 ppm
- Unhealthy: above 1,400 ppm
62%
of tram and light rail journeys stay at or below 800 ppm
Buses follow with 58% and metros with 52%.
13%
of regional train journeys average above 1,400 ppm
More than on any other mode. On long-distance trains, only 19% of journeys stay at or below 800 ppm, and their median of 1,013 ppm is the highest of all.
Long-distance trains: half of all ICE journeys average between 906 and 1,204 ppm, and only 0.7% average 2,000 ppm or more. Intercity trains have a longer tail: one journey in ten averages above 1,850 ppm. One EuroCity journey from Munich to Zurich averaged 8,441 ppm.
Public transport · All countries
Buses and trams get worse in winter, long-distance trains barely change
The same bus and tram lines average about 135 to 180 ppm more from October to March, and close to four in five of these lines are worse in winter. Long-distance trains stay between 1,030 and 1,060 ppm in both halves of the year, on the same 41 lines.
- April to September
- October to March
Activity by region
Where the data comes from
Vienna, Leipzig and Berlin lead
277 regions have at least one recording and 6 have more than 1,000, with California as the only one outside Europe. The top 10 regions hold 48% of all building recordings.
Check it yourself
All data behind these charts is open. Download it, explore it online or look at the code.
Raw data, public domain (CC0)
Code and documentation
Help us collect more data
The more places are measured, the clearer the picture gets: more countries, more place types and enough recordings to compare cities, chains and seasons. All you need is a portable CO2 monitor and the free app.
Contribute