In three years, spanning 2015 to 2018, the United Nations Environmental Programme (UNEP), estimates that 9.8m highly polluting second-hand vehicles were dumped in low-income countries in Africa, the Middle-East, Eastern Europe, Asia and Latin America.
High-income countries like the USA, the European Union and Japan are responsible for exporting 14 million second-hand vehicles across the globe within this period, and 70 per cent of them have made their way into poorer countries like Nigeria.
The UNEP, in a report, noted that more than 90 per cent of the cars imported into Kenya and the West African nation, were second-hand vehicles.
While Kenya has already started taking steps to cut down on its dirty car population, Nigeria is still delaying.
The New York Times reports that Kenya now accepts only imports of vehicles not more than eight years old, mainly from Japan.
Nigeria and its Economic Community of West African States (ECOWAS) counterparts, on the other hand, have set 2021 as the year to implement the European Union's most predated policy on polluting vehicles.
The EU mandated that cars built after 2005 should comply with Euro 4 standards, which required that the most harmful pollutants in car exhaust be reduced by more than 70 per cent in relation to those produced before the policy came into force.
The pollutants in question, fine particulate matter and nitrogen oxides, have been associated with increased risk of heart attacks, lung cancer and asthma.
Euro 4 has since been updated in 2009 and 2014, but ECOWAS is trying to implement the 2005 directive.
According to the UNEP report, 86 of the countries that import used cars, had "lax" or "very weak" laws around the age or environmental performance of used vehicles entering their markets.
Countries with stronger anti-emission regulations like the Netherlands have taken advantage of these 'wear' policies to import dirty cars into countries like Nigeria.
According to the New York Times, investigators found that some exporters in the Netherlands removed the pollution controls in the cars they exported, to harvest its metals.
Crude oil refiners in the Netherlands and Belgium, have also been accused of adding carcinogens into the dirty fuel exported to Nigeria to increase its quantity.
"What we found is not a pretty sight," Rob De Jong, an author of the report and head of the United Nations Environment Program's Sustainable Mobility Unit, was quoted as saying.
"Most of these vehicles are very old, very dirty, very inefficient and unsafe."
The report warned that the global trade in used vehicles could have stark consequences for both climate change and public health in the decades ahead, if left unsupervised.
Nigeria's policy supports the importation of dirty cars and petrol, making its environment one of the friendliest for fine particulate matter.