Balloon color and air quality

Why does the balloon change color?

In partnership with AIRPARIF®, the balloon reports two indices every two hours for the air quality in Paris:

  • the ambient air quality reported by the six AIRPARIF® “urban stations” in Paris using three projectors installed along the envelope’s equator.
  • the air quality near traffic reported by the five AIRPARIF® “traffic stations” in Paris using the extremely precise laser beam that sweeps the lower section of the balloon.

The indices are a simple and easily understandable way to show the quantity of three of the most problematic air pollutants in major European cities – nitrogen dioxide, ozone and particulates – according to the CITEAIR* index.

The envelope features two sets of icons: blinking cars and major Paris monuments.

The car and monument icons are visible day and night and are lit by 6,400 LED bulbs. Using the color code, they indicate the pollution levels both near traffic and in the ambient air based on the European CITEAR index provided in real time by AIRPARIF®

When the outline of the Eiffel Tower goes from green to yellow, this means that the ambient air quality has changed from good to fair.

The lights, which are powered by “clean” energy via a textile solar panel attached to the balloon envelope, are bright enough to be seen by 400,000 Parisians every day.


*Three years of research in partnership with around 30 cities and European experts as part of the CITEAIR project (Common Information To European AIR) were required to develop this index and make it available to the public. (

This index rounds out the information provided by the French ATMO index.