A bridge spanning a major road in Barcelona will be coated in photocatalytic concrete, allowing it to "eat" pollution.
The material uses energy from the sun to break down polluted air into little more than oxygen and water, keeping the bridge and air around it cleaner.
The high-tech concrete is part of a major redevelopment plan for Sarajevo bridge, which passes over Avinguda Meridiana on the northern approach to Barcelona. The project is the work of urban architecture firm BCQ.
As well as absorbing pollution the bridge will also be self-sufficient. Solar panels will be installed to generate energy for the bridge's LED lighting and the pavement will include a phosphorescent substance.
Vegetation and pergolas will provide shade and create a new space in the city for people to enjoy, BCQ said.
Photocatalytic concrete uses a titanium dioxide catalyst to break down smog and other pollution that has attached itself to the surface. This process, known as photocatalysis, neutralises pollution and turns it into oxygen, water, carbon dioxide, nitrate and sulfate. Rain then washes away the pollution, which means the concrete rarely needs cleaning with harmful industrial chemicals.
As well as keeping buildings and structures clean the material can also improve air quality. Similar technology is already used at the Air France offices at Charles-de-Gaulle airport near Paris and at the Church of the Year 2000 in Rome.
Carbon neutral and green architecture is becoming increasingly popular. One Central Park, a 33-storey building in Sydney, uses 40 motorised mirrors to redirect sunlight into shady areas and is covered in a living skin of 180,000 plants. In Milan the Bosco Verticale apartment complex, designed by architect Stefano Boeri, also uses plants and trees to absorb pollution and keep the building insulated.
The Barcelona bridge project is the work of architecture firm BCQ. It already has the backing of the city's government but no date has been set for its completion.