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 suggest the development of air pollution control capacities in large cities, emphasizing enforcement programmes using monitoring networks as appropriate.
The Metropolitan Air Quality Study of the Environment Protection Authority of New South Wales (1996), Australia identified motor vehicles and industry as the major sources of air pollutants. It also identified that peak ozone levels would need to be reduced by some 45% to achieve the recommended goal. Even greater reductions would be needed to counteract the effect of population growth. Initial analysis by the EPA indicates that strategies based on control and technological changes would, alone, not achieve the reductions in air pollution required. Strategies that target urban design and transport demand would be equally important.
In 1997, the US Environmental Protection Agency issued its "Ten-Year Air Quality and Emissions Trends" report. Carbon monoxide was down by 37 percent since 1986, lead was down by 78 percent, and particulate matter had dropped by nearly a quarter.