The City of London Corporation and King's College London have launched version 2.0 of the smartphone app which helps Londoners lower their impact on, and exposure to, air pollution.
Users can sign up for air pollution alerts and find low air pollution routes when levels of air pollution are high in London.
The CityAir app is currently available for iOS and Android and is compatible with iPhone, iPad and iPod touch and Android devices.
You can view a user's video for version 2.0 for iPhone and iPad.
It can be downloaded free of charge from the iTunes store and Google Play. A web based version is also available.