This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities. Agenda 21 suggests the development of air pollution control capacities in large cities, emphasizing enforcement programmes using monitoring networks as appropriate.
In 2018, Birmingham (UK) announced a plan to build “living green walls” along major commuter routes. According to research, the walls can remove at least 40 percent of nitrogen oxide and 60 percent of particulate matter from the surrounding air in urban canyons (referring to the confined areas of a city that are flanked by high walls made of concrete or glass, like roads with heavy traffic; since pollution gets trapped in an urban canyon, surrounding them with green walls full of grass, climbing ivy and other plants can help filter out toxic particles). The plans also include the construction of a green infrastructure network across Birmingham which would include urban forests, micro-parks, and use of new technology such as ‘City Trees'” – 13-foot frames of moss covering with the cleaning power of 275 trees. At least 900 deaths a year in Birmingham have been connected to air pollution via health conditions like cancer and heart and lung disease.