Mexico City was in the 1990s declared as the most polluted city in the world. In response, the government introduced a Management Plan to Improve Air Quality in the city. This involved investing in cleaner, unleaded fuels, tightening traffic restrictions and introducing catalytic convertors to all cars to reduce pollution.

This TV episode charts the successes of this initiative, which lead to a sharp decline in ozone emissions, particulates in the air and lead in children’s bloodstreams. It also recognises the challenges of continuing to reduce air pollution against rising costs of living and now that many feel the ‘worst’ of the pollution has already been overcome.

Assignment Earth is a five-part TV series exploring environmental issues affecting the world.