In 2009, I worked with Experientia on the Low2No project for the international SITRA competition to develop a neighborhood block called Jätkäsaari, in the city of Helsinki, Finland. Jätkäsaari was to be a stepping stone to aid Helsinki (and in turn, the world) to become carbon neutral/negative.
One of the concepts I worked on was the Pure Travel mobile service. Pure Travel would track your carbon usage by your mode of transport, and visualize how carbon heavy your day/week/month, etc., was. The change in smoke color due to personal action was meant as a deterrent in using more carbon heavy modes of transportation; a way to institute and create long lasting behavior change on the personal/individual level.